diff --git a/pyo3-derive-backend/src/pymethod.rs b/pyo3-derive-backend/src/pymethod.rs
index e47edc04..355a1e2e 100644
--- a/pyo3-derive-backend/src/pymethod.rs
+++ b/pyo3-derive-backend/src/pymethod.rs
@@ -222,7 +222,11 @@ pub fn impl_proto_wrap(cls: &syn::Type, name: &syn::Ident, spec: &FnSpec<'_>) ->
 pub fn impl_wrap_new(cls: &syn::Type, name: &syn::Ident, spec: &FnSpec<'_>) -> TokenStream {
     let names: Vec<syn::Ident> = get_arg_names(&spec);
     let cb = quote! { #cls::#name(#(#names),*) };
-    let body = impl_arg_params(spec, cb);
+    let body = impl_arg_params_(
+        spec,
+        cb,
+        quote! { pyo3::pyclass::IntoInitializer::into_initializer },
+    );
 
     quote! {
         #[allow(unused_mut)]
@@ -239,9 +243,9 @@ pub fn impl_wrap_new(cls: &syn::Type, name: &syn::Ident, spec: &FnSpec<'_>) -> T
             let _args = _py.from_borrowed_ptr::<pyo3::types::PyTuple>(_args);
             let _kwargs: Option<&pyo3::types::PyDict> = _py.from_borrowed_ptr_or_opt(_kwargs);
 
-            # body
+            #body
 
-            match _result.and_then(|slf| pyo3::PyClassShell::new(_py, slf)) {
+            match _result.and_then(|init| init.create_shell(_py)) {
                 Ok(slf) => slf as _,
                 Err(e) => e.restore_and_null(_py),
             }
@@ -409,11 +413,11 @@ fn bool_to_ident(condition: bool) -> syn::Ident {
     }
 }
 
-pub fn impl_arg_params(spec: &FnSpec<'_>, body: TokenStream) -> TokenStream {
+fn impl_arg_params_(spec: &FnSpec<'_>, body: TokenStream, into_result: TokenStream) -> TokenStream {
     if spec.args.is_empty() {
         return quote! {
             let _result = {
-                pyo3::derive_utils::IntoPyResult::into_py_result(#body)
+                #into_result (#body)
             };
         };
     }
@@ -471,11 +475,19 @@ pub fn impl_arg_params(spec: &FnSpec<'_>, body: TokenStream) -> TokenStream {
 
             #(#param_conversion)*
 
-            pyo3::derive_utils::IntoPyResult::into_py_result(#body)
+            #into_result(#body)
         })();
     }
 }
 
+pub fn impl_arg_params(spec: &FnSpec<'_>, body: TokenStream) -> TokenStream {
+    impl_arg_params_(
+        spec,
+        body,
+        quote! { pyo3::derive_utils::IntoPyResult::into_py_result },
+    )
+}
+
 /// Re option_pos: The option slice doesn't contain the py: Python argument, so the argument
 /// index and the index in option diverge when using py: Python
 fn impl_arg_param(
diff --git a/src/derive_utils.rs b/src/derive_utils.rs
index c1a9ac32..f64cde0d 100644
--- a/src/derive_utils.rs
+++ b/src/derive_utils.rs
@@ -9,9 +9,7 @@ use crate::exceptions::TypeError;
 use crate::init_once;
 use crate::instance::PyNativeType;
 use crate::types::{PyAny, PyDict, PyModule, PyTuple};
-use crate::GILPool;
-use crate::Python;
-use crate::{ffi, IntoPy, PyObject};
+use crate::{ffi, GILPool, IntoPy, PyObject, Python};
 use std::ptr;
 
 /// Description of a python parameter; used for `parse_args()`.
diff --git a/src/instance.rs b/src/instance.rs
index 9c728ecb..b91f2786 100644
--- a/src/instance.rs
+++ b/src/instance.rs
@@ -3,7 +3,7 @@ use crate::err::{PyErr, PyResult};
 use crate::gil;
 use crate::object::PyObject;
 use crate::objectprotocol::ObjectProtocol;
-use crate::pyclass::{PyClass, PyClassShell};
+use crate::pyclass::{IntoInitializer, PyClass, PyClassShell};
 use crate::type_object::{PyConcreteObject, PyTypeInfo};
 use crate::types::PyAny;
 use crate::{ffi, IntoPy};
@@ -35,11 +35,12 @@ unsafe impl<T> Sync for Py<T> {}
 
 impl<T> Py<T> {
     /// Create new instance of T and move it under python management
-    pub fn new(py: Python, value: T) -> PyResult<Py<T>>
+    pub fn new(py: Python, value: impl IntoInitializer<T>) -> PyResult<Py<T>>
     where
-        T: PyClass,
+        T: PyClass + PyTypeInfo<ConcreteLayout = PyClassShell<T>>,
     {
-        let obj = unsafe { PyClassShell::new(py, value)? };
+        let initializer = value.into_initializer()?;
+        let obj = unsafe { initializer.create_shell(py)? };
         let ob = unsafe { Py::from_owned_ptr(obj as _) };
         Ok(ob)
     }
diff --git a/src/lib.rs b/src/lib.rs
index 88d62b69..383f753f 100755
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -127,7 +127,7 @@ pub use crate::gil::{init_once, GILGuard, GILPool};
 pub use crate::instance::{AsPyRef, ManagedPyRef, Py, PyNativeType};
 pub use crate::object::PyObject;
 pub use crate::objectprotocol::ObjectProtocol;
-pub use crate::pyclass::{PyClass, PyClassShell};
+pub use crate::pyclass::{PyClass, PyClassInitializer, PyClassShell};
 pub use crate::python::{prepare_freethreaded_python, Python};
 pub use crate::type_object::{type_flags, PyConcreteObject, PyTypeInfo};
 
@@ -217,7 +217,7 @@ macro_rules! wrap_pymodule {
 ///
 /// # Example
 /// ```
-/// use pyo3::{prelude::*, py_run};
+/// use pyo3::{prelude::*, py_run, PyClassShell};
 /// #[pyclass]
 /// #[derive(Debug)]
 /// struct Time {
@@ -240,7 +240,7 @@ macro_rules! wrap_pymodule {
 /// }
 /// let gil = Python::acquire_gil();
 /// let py = gil.python();
-/// let time = PyRef::new(py, Time {hour: 8, minute: 43, second: 16}).unwrap();
+/// let time = PyClassShell::new_ref(py, Time {hour: 8, minute: 43, second: 16}).unwrap();
 /// let time_as_tuple = (8, 43, 16);
 /// py_run!(py, time time_as_tuple, r#"
 /// assert time.hour == 8
diff --git a/src/prelude.rs b/src/prelude.rs
index 821bc939..4b4cd038 100644
--- a/src/prelude.rs
+++ b/src/prelude.rs
@@ -18,6 +18,7 @@ pub use crate::objectprotocol::ObjectProtocol;
 pub use crate::python::Python;
 pub use crate::{FromPy, FromPyObject, IntoPy, IntoPyPointer, PyTryFrom, PyTryInto, ToPyObject};
 // This is only part of the prelude because we need it for the pymodule function
+pub use crate::pyclass::PyClassInitializer;
 pub use crate::types::PyModule;
 pub use pyo3cls::pymodule;
 pub use pyo3cls::{pyclass, pyfunction, pymethods, pyproto};
diff --git a/src/pyclass.rs b/src/pyclass.rs
index eba23e2c..074d13f7 100644
--- a/src/pyclass.rs
+++ b/src/pyclass.rs
@@ -1,6 +1,7 @@
 //! An experiment module which has all codes related only to #[pyclass]
 use crate::class::methods::{PyMethodDefType, PyMethodsProtocol};
 use crate::conversion::{AsPyPointer, FromPyPointer, ToPyObject};
+use crate::exceptions::RuntimeError;
 use crate::pyclass_slots::{PyClassDict, PyClassWeakRef};
 use crate::type_object::{type_flags, PyConcreteObject, PyTypeObject};
 use crate::types::PyAny;
@@ -75,7 +76,7 @@ where
     }
 }
 
-/// So this is a shell for our *sweet* pyclasses to survive in *harsh* Python world.
+/// `PyClassShell` represents the concrete layout of our `#[pyclass]` in the Python heap.
 #[repr(C)]
 pub struct PyClassShell<T: PyClass> {
     ob_base: <T::BaseType as PyTypeInfo>::ConcreteLayout,
@@ -85,28 +86,37 @@ pub struct PyClassShell<T: PyClass> {
 }
 
 impl<T: PyClass> PyClassShell<T> {
-    pub fn new_ref(py: Python, value: T) -> PyResult<&Self> {
+    pub fn new_ref(py: Python, value: impl IntoInitializer<T>) -> PyResult<&Self>
+    where
+        T: PyTypeInfo<ConcreteLayout = Self>,
+    {
         unsafe {
-            let ptr = Self::new(py, value)?;
-            FromPyPointer::from_owned_ptr_or_err(py, ptr as _)
+            let initializer = value.into_initializer()?;
+            let self_ = initializer.create_shell(py)?;
+            FromPyPointer::from_owned_ptr_or_err(py, self_ as _)
         }
     }
 
-    pub fn new_mut(py: Python, value: T) -> PyResult<&mut Self> {
+    pub fn new_mut(py: Python, value: impl IntoInitializer<T>) -> PyResult<&mut Self>
+    where
+        T: PyTypeInfo<ConcreteLayout = Self>,
+    {
         unsafe {
-            let ptr = Self::new(py, value)?;
-            FromPyPointer::from_owned_ptr_or_err(py, ptr as _)
+            let initializer = value.into_initializer()?;
+            let self_ = initializer.create_shell(py)?;
+            FromPyPointer::from_owned_ptr_or_err(py, self_ as _)
         }
     }
 
-    pub unsafe fn new(py: Python, value: T) -> PyResult<*mut Self> {
+    #[doc(hidden)]
+    unsafe fn new(py: Python) -> PyResult<*mut Self> {
+        <T::BaseType as PyTypeObject>::init_type();
         T::init_type();
         let base = T::alloc(py);
         if base.is_null() {
             return Err(PyErr::fetch(py));
         }
         let self_ = base as *mut Self;
-        (*self_).pyclass = ManuallyDrop::new(value);
         (*self_).dict = T::Dict::new();
         (*self_).weakref = T::WeakRef::new();
         Ok(self_)
@@ -114,13 +124,14 @@ impl<T: PyClass> PyClassShell<T> {
 }
 
 impl<T: PyClass> PyConcreteObject<T> for PyClassShell<T> {
+    const NEED_INIT: bool = std::mem::size_of::<T>() != 0;
     unsafe fn internal_ref_cast(obj: &PyAny) -> &T {
         let shell = obj.as_ptr() as *const PyClassShell<T>;
-        &*(*shell).pyclass
+        &(*shell).pyclass
     }
     unsafe fn internal_mut_cast(obj: &PyAny) -> &mut T {
         let shell = obj.as_ptr() as *const PyClassShell<T> as *mut PyClassShell<T>;
-        &mut *(*shell).pyclass
+        &mut (*shell).pyclass
     }
     unsafe fn py_drop(&mut self, py: Python) {
         ManuallyDrop::drop(&mut self.pyclass);
@@ -128,6 +139,12 @@ impl<T: PyClass> PyConcreteObject<T> for PyClassShell<T> {
         self.weakref.clear_weakrefs(self.as_ptr(), py);
         self.ob_base.py_drop(py);
     }
+    unsafe fn py_init(&mut self, value: T) {
+        self.pyclass = ManuallyDrop::new(value);
+    }
+    fn get_super(&mut self) -> Option<&mut <T::BaseType as PyTypeInfo>::ConcreteLayout> {
+        Some(&mut self.ob_base)
+    }
 }
 
 impl<T: PyClass> AsPyPointer for PyClassShell<T> {
@@ -190,6 +207,108 @@ where
     }
 }
 
+/// An initializer for `PyClassShell<T>`.
+///
+/// **NOTE** If
+pub struct PyClassInitializer<T: PyTypeInfo> {
+    init: Option<T>,
+    super_init: Option<*mut PyClassInitializer<T::BaseType>>,
+}
+
+impl<T: PyTypeInfo> PyClassInitializer<T> {
+    pub fn from_value(value: T) -> Self {
+        PyClassInitializer {
+            init: Some(value),
+            super_init: None,
+        }
+    }
+
+    pub fn new() -> Self {
+        PyClassInitializer {
+            init: None,
+            super_init: None,
+        }
+    }
+
+    #[must_use]
+    #[doc(hiddden)]
+    pub fn init_class(self, shell: &mut T::ConcreteLayout) -> PyResult<()> {
+        macro_rules! raise_err {
+            ($name: path) => {
+                return Err(PyErr::new::<RuntimeError, _>(format!(
+                    "Base class '{}' is not initialized",
+                    $name
+                )));
+            };
+        }
+        let PyClassInitializer { init, super_init } = self;
+        if let Some(value) = init {
+            unsafe { shell.py_init(value) };
+        } else if !T::ConcreteLayout::NEED_INIT {
+            raise_err!(T::NAME);
+        }
+        if let Some(super_init) = super_init {
+            let super_init = unsafe { Box::from_raw(super_init) };
+            if let Some(super_obj) = shell.get_super() {
+                super_init.init_class(super_obj)?;
+            }
+        } else if <T::BaseType as PyTypeInfo>::ConcreteLayout::NEED_INIT {
+            raise_err!(T::BaseType::NAME)
+        }
+        Ok(())
+    }
+
+    pub fn init(&mut self, value: T) {
+        self.init = Some(value);
+    }
+
+    pub fn get_super(&mut self) -> &mut PyClassInitializer<T::BaseType> {
+        if let Some(super_init) = self.super_init {
+            return unsafe { &mut *super_init };
+        }
+        let super_init = Box::into_raw(Box::new(PyClassInitializer::new()));
+        self.super_init = Some(super_init);
+        return unsafe { &mut *super_init };
+    }
+
+    pub unsafe fn create_shell(self, py: Python) -> PyResult<*mut PyClassShell<T>>
+    where
+        T: PyClass + PyTypeInfo<ConcreteLayout = PyClassShell<T>>,
+    {
+        let shell = PyClassShell::new(py)?;
+        self.init_class(&mut *shell)?;
+        Ok(shell)
+    }
+}
+
+pub trait IntoInitializer<T: PyTypeInfo> {
+    fn into_initializer(self) -> PyResult<PyClassInitializer<T>>;
+}
+
+impl<T: PyTypeInfo> IntoInitializer<T> for T {
+    fn into_initializer(self) -> PyResult<PyClassInitializer<T>> {
+        Ok(PyClassInitializer::from_value(self))
+    }
+}
+
+impl<T: PyTypeInfo> IntoInitializer<T> for PyResult<T> {
+    fn into_initializer(self) -> PyResult<PyClassInitializer<T>> {
+        self.map(PyClassInitializer::from_value)
+    }
+}
+
+impl<T: PyTypeInfo> IntoInitializer<T> for PyClassInitializer<T> {
+    fn into_initializer(self) -> PyResult<PyClassInitializer<T>> {
+        Ok(self)
+    }
+}
+
+impl<T: PyTypeInfo> IntoInitializer<T> for PyResult<PyClassInitializer<T>> {
+    fn into_initializer(self) -> PyResult<PyClassInitializer<T>> {
+        self
+    }
+}
+
 /// Register new type in python object system.
 #[cfg(not(Py_LIMITED_API))]
 pub fn initialize_type<T>(py: Python, module_name: Option<&str>) -> PyResult<*mut ffi::PyTypeObject>
diff --git a/src/type_object.rs b/src/type_object.rs
index 4b939716..39768602 100644
--- a/src/type_object.rs
+++ b/src/type_object.rs
@@ -12,7 +12,8 @@ use crate::Python;
 use std::ptr::NonNull;
 
 /// TODO: write document
-pub trait PyConcreteObject<T>: Sized {
+pub trait PyConcreteObject<T: PyTypeInfo>: Sized {
+    const NEED_INIT: bool = false;
     unsafe fn internal_ref_cast(obj: &PyAny) -> &T {
         &*(obj as *const _ as *const T)
     }
@@ -20,9 +21,13 @@ pub trait PyConcreteObject<T>: Sized {
         &mut *(obj as *const _ as *const T as *mut T)
     }
     unsafe fn py_drop(&mut self, _py: Python) {}
+    unsafe fn py_init(&mut self, _value: T) {}
+    fn get_super(&mut self) -> Option<&mut <T::BaseType as PyTypeInfo>::ConcreteLayout> {
+        None
+    }
 }
 
-impl<T: PyNativeType> PyConcreteObject<T> for ffi::PyObject {}
+impl<T: PyNativeType + PyTypeInfo> PyConcreteObject<T> for ffi::PyObject {}
 
 /// Our custom type flags
 pub mod type_flags {
@@ -57,7 +62,7 @@ pub trait PyTypeInfo: Sized {
     const FLAGS: usize = 0;
 
     /// Base class
-    type BaseType: PyTypeInfo;
+    type BaseType: PyTypeInfo + PyTypeObject;
 
     /// Layout
     type ConcreteLayout: PyConcreteObject<Self>;
diff --git a/tests/test_dunder.rs b/tests/test_dunder.rs
index 6bb177cf..6fecc4c7 100755
--- a/tests/test_dunder.rs
+++ b/tests/test_dunder.rs
@@ -57,7 +57,7 @@ impl<'p> PyIterProtocol for Iterator {
         Ok(slf.into())
     }
 
-    fn __next__(mut slf: &mut PyClassShell<Self>) -> PyResult<Option<i32>> {
+    fn __next__(slf: &mut PyClassShell<Self>) -> PyResult<Option<i32>> {
         Ok(slf.iter.next())
     }
 }
diff --git a/tests/test_gc.rs b/tests/test_gc.rs
index 81fa8963..cac90a79 100644
--- a/tests/test_gc.rs
+++ b/tests/test_gc.rs
@@ -3,7 +3,7 @@ use pyo3::class::PyTraverseError;
 use pyo3::class::PyVisit;
 use pyo3::prelude::*;
 use pyo3::types::{PyAny, PyTuple};
-use pyo3::{ffi, py_run, AsPyPointer, PyClassShell};
+use pyo3::{ffi, py_run, AsPyPointer, PyClassInitializer, PyClassShell};
 use std::cell::RefCell;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
@@ -235,10 +235,11 @@ struct SubClassWithDrop {
 
 #[pymethods]
 impl SubClassWithDrop {
-    // TODO(kngwyu): Implement baseclass initialization
     #[new]
-    fn new() -> SubClassWithDrop {
-        SubClassWithDrop { data: None }
+    fn new() -> PyClassInitializer<Self> {
+        let mut init = PyClassInitializer::from_value(SubClassWithDrop { data: None });
+        init.get_super().init(BaseClassWithDrop { data: None });
+        init
     }
 }
 
diff --git a/tests/test_getter_setter.rs b/tests/test_getter_setter.rs
index cacf5652..7610e81f 100644
--- a/tests/test_getter_setter.rs
+++ b/tests/test_getter_setter.rs
@@ -1,7 +1,6 @@
 use pyo3::prelude::*;
 use pyo3::py_run;
 use pyo3::types::{IntoPyDict, PyList};
-use std::isize;
 
 mod common;
 
diff --git a/tests/test_inheritance.rs b/tests/test_inheritance.rs
index 462ff138..14aed197 100644
--- a/tests/test_inheritance.rs
+++ b/tests/test_inheritance.rs
@@ -1,5 +1,6 @@
 use pyo3::prelude::*;
 use pyo3::py_run;
+
 #[cfg(feature = "unsound-subclass")]
 use pyo3::types::IntoPyDict;
 
@@ -48,19 +49,58 @@ struct SubClass {
 #[pymethods]
 impl SubClass {
     #[new]
-    fn new() -> Self {
-        SubClass { val2: 5 }
+    fn new() -> PyClassInitializer<Self> {
+        let mut init = PyClassInitializer::from_value(SubClass { val2: 5 });
+        init.get_super().init(BaseClass { val1: 10 });
+        init
     }
 }
 
-// TODO(kngwyu): disable untill super().__init__ fixed
 #[test]
-#[ignore]
 fn inheritance_with_new_methods() {
     let gil = Python::acquire_gil();
     let py = gil.python();
-    let _typebase = py.get_type::<BaseClass>();
+    let _baseobj = py.get_type::<BaseClass>();
     let typeobj = py.get_type::<SubClass>();
     let inst = typeobj.call((), None).unwrap();
     py_run!(py, inst, "assert inst.val1 == 10; assert inst.val2 == 5");
 }
+
+#[pyclass(extends=BaseClass)]
+struct InvalidSubClass {
+    #[pyo3(get)]
+    val2: usize,
+}
+
+#[pymethods]
+impl InvalidSubClass {
+    #[new]
+    fn new() -> PyClassInitializer<Self> {
+        PyClassInitializer::from_value(InvalidSubClass { val2: 5 })
+    }
+}
+
+#[test]
+fn uninit_baseclass_raise_exception() {
+    let gil = Python::acquire_gil();
+    let py = gil.python();
+    let _baseclass = py.get_type::<BaseClass>();
+    let subclass = py.get_type::<InvalidSubClass>();
+    py_expect_exception!(py, subclass, "subclass()", RuntimeError);
+}
+
+#[test]
+fn uninit_baseclass_returns_err() {
+    let gil = Python::acquire_gil();
+    let py = gil.python();
+    let subclass = pyo3::pyclass::PyClassShell::new_ref(py, InvalidSubClass { val2: 5 });
+    if let Err(err) = subclass {
+        py_run!(
+            py,
+            err,
+            r#"str(err) == "Base class 'BaseClass' is not initialized""#
+        )
+    } else {
+        panic!("Uninitialized class detection failed!!!")
+    }
+}