diff --git a/python-package/lightgbm/basic.py b/python-package/lightgbm/basic.py
index 5a1c9c7b9609..047a76fb6c34 100644
--- a/python-package/lightgbm/basic.py
+++ b/python-package/lightgbm/basic.py
@@ -237,7 +237,7 @@ def _data_to_2d_numpy(data: Any, dtype: type = np.float32, name: str = 'list') -
                     "It should be list of lists, numpy 2-D array or pandas DataFrame")
 
 
-def cfloat32_array_to_numpy(cptr, length):
+def cfloat32_array_to_numpy(cptr: ctypes.POINTER, length: int) -> np.ndarray:
     """Convert a ctypes float pointer array to a numpy array."""
     if isinstance(cptr, ctypes.POINTER(ctypes.c_float)):
         return np.ctypeslib.as_array(cptr, shape=(length,)).copy()
@@ -245,7 +245,7 @@ def cfloat32_array_to_numpy(cptr, length):
         raise RuntimeError('Expected float pointer')
 
 
-def cfloat64_array_to_numpy(cptr, length):
+def cfloat64_array_to_numpy(cptr: ctypes.POINTER, length: int) -> np.ndarray:
     """Convert a ctypes double pointer array to a numpy array."""
     if isinstance(cptr, ctypes.POINTER(ctypes.c_double)):
         return np.ctypeslib.as_array(cptr, shape=(length,)).copy()
@@ -253,7 +253,7 @@ def cfloat64_array_to_numpy(cptr, length):
         raise RuntimeError('Expected double pointer')
 
 
-def cint32_array_to_numpy(cptr, length):
+def cint32_array_to_numpy(cptr: ctypes.POINTER, length: int) -> np.ndarray:
     """Convert a ctypes int pointer array to a numpy array."""
     if isinstance(cptr, ctypes.POINTER(ctypes.c_int32)):
         return np.ctypeslib.as_array(cptr, shape=(length,)).copy()
@@ -261,7 +261,7 @@ def cint32_array_to_numpy(cptr, length):
         raise RuntimeError('Expected int32 pointer')
 
 
-def cint64_array_to_numpy(cptr, length):
+def cint64_array_to_numpy(cptr: ctypes.POINTER, length: int) -> np.ndarray:
     """Convert a ctypes int pointer array to a numpy array."""
     if isinstance(cptr, ctypes.POINTER(ctypes.c_int64)):
         return np.ctypeslib.as_array(cptr, shape=(length,)).copy()
@@ -269,12 +269,12 @@ def cint64_array_to_numpy(cptr, length):
         raise RuntimeError('Expected int64 pointer')
 
 
-def c_str(string):
+def c_str(string: str) -> ctypes.c_char_p:
     """Convert a Python string to C string."""
     return ctypes.c_char_p(string.encode('utf-8'))
 
 
-def c_array(ctype, values):
+def c_array(ctype: type, values: List[Any]) -> ctypes.Array:
     """Convert a Python array to C array."""
     return (ctype * len(values))(*values)