diff --git a/CHANGES b/CHANGES
index bdd2fb152ce..33d20a45bf5 100644
--- a/CHANGES
+++ b/CHANGES
@@ -71,6 +71,8 @@ Bugs fixed
 * #9756: autodoc: Crashed if classmethod does not have __func__ attribute
 * #9757: autodoc: :confval:`autodoc_inherit_docstrings` does not effect to
   overriden classmethods
+* #9781: autodoc: :confval:`autodoc_preserve_defaults` does not support
+  hexadecimal numeric
 * #9630: autosummary: Failed to build summary table if :confval:`primary_domain`
   is not 'py'
 * #9670: html: Fix download file with special characters
diff --git a/sphinx/ext/autodoc/preserve_defaults.py b/sphinx/ext/autodoc/preserve_defaults.py
index 3d859fe8eee..d451d0973ce 100644
--- a/sphinx/ext/autodoc/preserve_defaults.py
+++ b/sphinx/ext/autodoc/preserve_defaults.py
@@ -11,7 +11,8 @@
 
 import ast
 import inspect
-from typing import Any, Dict
+import sys
+from typing import Any, Dict, List, Optional
 
 from sphinx.application import Sphinx
 from sphinx.locale import __
@@ -49,11 +50,32 @@ def get_function_def(obj: Any) -> ast.FunctionDef:
         return None
 
 
+def get_default_value(lines: List[str], position: ast.AST) -> Optional[str]:
+    try:
+        if sys.version_info < (3, 8):  # only for py38+
+            return None
+        elif position.lineno == position.end_lineno:
+            line = lines[position.lineno - 1]
+            return line[position.col_offset:position.end_col_offset]
+        else:
+            # multiline value is not supported now
+            return None
+    except (AttributeError, IndexError):
+        return None
+
+
 def update_defvalue(app: Sphinx, obj: Any, bound_method: bool) -> None:
     """Update defvalue info of *obj* using type_comments."""
     if not app.config.autodoc_preserve_defaults:
         return
 
+    try:
+        lines = inspect.getsource(obj).splitlines()
+        if lines[0].startswith((' ', r'\t')):
+            lines.insert(0, '')  # insert a dummy line to follow what get_function_def() does.
+    except OSError:
+        lines = []
+
     try:
         function = get_function_def(obj)
         if function.args.defaults or function.args.kw_defaults:
@@ -64,11 +86,17 @@ def update_defvalue(app: Sphinx, obj: Any, bound_method: bool) -> None:
             for i, param in enumerate(parameters):
                 if param.default is not param.empty:
                     if param.kind in (param.POSITIONAL_ONLY, param.POSITIONAL_OR_KEYWORD):
-                        value = DefaultValue(ast_unparse(defaults.pop(0)))  # type: ignore
-                        parameters[i] = param.replace(default=value)
+                        default = defaults.pop(0)
+                        value = get_default_value(lines, default)
+                        if value is None:
+                            value = ast_unparse(default)  # type: ignore
+                        parameters[i] = param.replace(default=DefaultValue(value))
                     else:
-                        value = DefaultValue(ast_unparse(kw_defaults.pop(0)))  # type: ignore
-                        parameters[i] = param.replace(default=value)
+                        default = kw_defaults.pop(0)
+                        value = get_default_value(lines, default)
+                        if value is None:
+                            value = ast_unparse(default)  # type: ignore
+                        parameters[i] = param.replace(default=DefaultValue(value))
             sig = sig.replace(parameters=parameters)
             obj.__signature__ = sig
     except (AttributeError, TypeError):
diff --git a/tests/roots/test-ext-autodoc/target/preserve_defaults.py b/tests/roots/test-ext-autodoc/target/preserve_defaults.py
index 79305349b40..422d41b953a 100644
--- a/tests/roots/test-ext-autodoc/target/preserve_defaults.py
+++ b/tests/roots/test-ext-autodoc/target/preserve_defaults.py
@@ -7,7 +7,8 @@
 
 def foo(name: str = CONSTANT,
         sentinel: Any = SENTINEL,
-        now: datetime = datetime.now()) -> None:
+        now: datetime = datetime.now(),
+        color: int = 0xFFFFFF) -> None:
     """docstring"""
 
 
@@ -15,5 +16,5 @@ class Class:
     """docstring"""
 
     def meth(self, name: str = CONSTANT, sentinel: Any = SENTINEL,
-             now: datetime = datetime.now()) -> None:
+             now: datetime = datetime.now(), color: int = 0xFFFFFF) -> None:
         """docstring"""
diff --git a/tests/test_ext_autodoc_preserve_defaults.py b/tests/test_ext_autodoc_preserve_defaults.py
index c0b5a9f294f..955c60aa4bf 100644
--- a/tests/test_ext_autodoc_preserve_defaults.py
+++ b/tests/test_ext_autodoc_preserve_defaults.py
@@ -8,6 +8,8 @@
     :license: BSD, see LICENSE for details.
 """
 
+import sys
+
 import pytest
 
 from .test_ext_autodoc import do_autodoc
@@ -16,6 +18,11 @@
 @pytest.mark.sphinx('html', testroot='ext-autodoc',
                     confoverrides={'autodoc_preserve_defaults': True})
 def test_preserve_defaults(app):
+    if sys.version_info < (3, 8):
+        color = "16777215"
+    else:
+        color = "0xFFFFFF"
+
     options = {"members": None}
     actual = do_autodoc(app, 'module', 'target.preserve_defaults', options)
     assert list(actual) == [
@@ -30,14 +37,14 @@ def test_preserve_defaults(app):
         '',
         '',
         '   .. py:method:: Class.meth(name: str = CONSTANT, sentinel: Any = SENTINEL, '
-        'now: datetime.datetime = datetime.now()) -> None',
+        'now: datetime.datetime = datetime.now(), color: int = %s) -> None' % color,
         '      :module: target.preserve_defaults',
         '',
         '      docstring',
         '',
         '',
         '.. py:function:: foo(name: str = CONSTANT, sentinel: Any = SENTINEL, now: '
-        'datetime.datetime = datetime.now()) -> None',
+        'datetime.datetime = datetime.now(), color: int = %s) -> None' % color,
         '   :module: target.preserve_defaults',
         '',
         '   docstring',