diff --git a/packages/markitdown/src/markitdown/converters/_docx_converter.py b/packages/markitdown/src/markitdown/converters/_docx_converter.py
index 3975107b1..7b7fef9a6 100644
--- a/packages/markitdown/src/markitdown/converters/_docx_converter.py
+++ b/packages/markitdown/src/markitdown/converters/_docx_converter.py
@@ -26,6 +26,7 @@
 ]
 
 ACCEPTED_FILE_EXTENSIONS = [".docx"]
+DEFAULT_STYLE_MAP = "u => u"
 
 
 class DocxConverter(HtmlConverter):
@@ -75,7 +76,12 @@ def convert(
                 _dependency_exc_info[2]
             )
 
-        style_map = kwargs.get("style_map", None)
+        style_map = kwargs.get("style_map")
+        if style_map:
+            style_map = f"{DEFAULT_STYLE_MAP}\n{style_map}"
+        else:
+            style_map = DEFAULT_STYLE_MAP
+
         pre_process_stream = pre_process_docx(file_stream)
         return self._html_converter.convert_string(
             mammoth.convert_to_html(pre_process_stream, style_map=style_map).value,
diff --git a/packages/markitdown/tests/test_module_misc.py b/packages/markitdown/tests/test_module_misc.py
index 8e3acc23d..73451cc30 100644
--- a/packages/markitdown/tests/test_module_misc.py
+++ b/packages/markitdown/tests/test_module_misc.py
@@ -5,8 +5,11 @@
 import shutil
 import pytest
 from unittest.mock import MagicMock
+from types import SimpleNamespace
 
 from markitdown._uri_utils import parse_data_uri, file_uri_to_path
+from markitdown.converters._docx_converter import DocxConverter, DEFAULT_STYLE_MAP
+from markitdown.converters import _docx_converter
 
 from markitdown import (
     MarkItDown,
@@ -261,6 +264,56 @@ def test_docx_comments() -> None:
     validate_strings(result, DOCX_COMMENT_TEST_STRINGS)
 
 
+def test_docx_converter_preserves_underline_by_default(monkeypatch) -> None:
+    converter = DocxConverter()
+    captured = {}
+
+    monkeypatch.setattr(_docx_converter, "pre_process_docx", lambda stream: stream)
+
+    def fake_convert_to_html(stream, style_map=None):
+        captured["style_map"] = style_map
+        return SimpleNamespace(value="<p><u>underlined</u></p>")
+
+    monkeypatch.setattr(_docx_converter.mammoth, "convert_to_html", fake_convert_to_html)
+    monkeypatch.setattr(
+        converter._html_converter,
+        "convert_string",
+        lambda html, **kwargs: html,
+    )
+
+    result = converter.convert(io.BytesIO(b"docx"), StreamInfo(extension=".docx"))
+
+    assert captured["style_map"] == DEFAULT_STYLE_MAP
+    assert result == "<p><u>underlined</u></p>"
+
+
+def test_docx_converter_appends_custom_style_map(monkeypatch) -> None:
+    converter = DocxConverter()
+    captured = {}
+
+    monkeypatch.setattr(_docx_converter, "pre_process_docx", lambda stream: stream)
+
+    def fake_convert_to_html(stream, style_map=None):
+        captured["style_map"] = style_map
+        return SimpleNamespace(value="<p>comment</p>")
+
+    monkeypatch.setattr(_docx_converter.mammoth, "convert_to_html", fake_convert_to_html)
+    monkeypatch.setattr(
+        converter._html_converter,
+        "convert_string",
+        lambda html, **kwargs: html,
+    )
+
+    result = converter.convert(
+        io.BytesIO(b"docx"),
+        StreamInfo(extension=".docx"),
+        style_map="comment-reference => ",
+    )
+
+    assert captured["style_map"] == f"{DEFAULT_STYLE_MAP}\ncomment-reference => "
+    assert result == "<p>comment</p>"
+
+
 def test_docx_equations() -> None:
     markitdown = MarkItDown()
     docx_file = os.path.join(TEST_FILES_DIR, "equations.docx")