diff --git a/Doc/whatsnew/3.15.rst b/Doc/whatsnew/3.15.rst
index 56028a92aa2e29..6a8f037035866b 100644
--- a/Doc/whatsnew/3.15.rst
+++ b/Doc/whatsnew/3.15.rst
@@ -682,6 +682,8 @@ mimetypes
 ---------
 
 * Add ``application/toml``. (Contributed by Gil Forcada in :gh:`139959`.)
+* Rename ``application/x-texinfo`` to ``application/texinfo``.
+  (Contributed by Charlie Lin in :gh:`140165`)
 
 
 pathlib
diff --git a/Lib/mimetypes.py b/Lib/mimetypes.py
index 6c0efb671975d4..48a9f430d45262 100644
--- a/Lib/mimetypes.py
+++ b/Lib/mimetypes.py
@@ -500,6 +500,8 @@ def _default_mime_types():
         '.ps'     : 'application/postscript',
         '.ai'     : 'application/postscript',
         '.eps'    : 'application/postscript',
+        '.texi'   : 'application/texinfo',
+        '.texinfo': 'application/texinfo',
         '.toml'   : 'application/toml',
         '.trig'   : 'application/trig',
         '.m3u'    : 'application/vnd.apple.mpegurl',
@@ -549,8 +551,6 @@ def _default_mime_types():
         '.tar'    : 'application/x-tar',
         '.tcl'    : 'application/x-tcl',
         '.tex'    : 'application/x-tex',
-        '.texi'   : 'application/x-texinfo',
-        '.texinfo': 'application/x-texinfo',
         '.roff'   : 'application/x-troff',
         '.t'      : 'application/x-troff',
         '.tr'     : 'application/x-troff',
diff --git a/Lib/test/test_mimetypes.py b/Lib/test/test_mimetypes.py
index a29815bf49b1e7..746984ec0ca9df 100644
--- a/Lib/test/test_mimetypes.py
+++ b/Lib/test/test_mimetypes.py
@@ -230,6 +230,7 @@ def check_extensions():
                 ("application/gzip", ".gz"),
                 ("application/ogg", ".ogx"),
                 ("application/postscript", ".ps"),
+                ("application/texinfo", ".texi"),
                 ("application/toml", ".toml"),
                 ("application/vnd.apple.mpegurl", ".m3u"),
                 ("application/vnd.ms-excel", ".xls"),
@@ -247,7 +248,6 @@ def check_extensions():
                 ("application/x-debian-package", ".deb"),
                 ("application/x-httpd-php", ".php"),
                 ("application/x-rpm", ".rpm"),
-                ("application/x-texinfo", ".texi"),
                 ("application/x-troff", ".roff"),
                 ("application/xml", ".xsl"),
                 ("application/yaml", ".yaml"),
diff --git a/Misc/NEWS.d/next/Library/2025-10-15-15-10-34.gh-issue-140166.NtxRez.rst b/Misc/NEWS.d/next/Library/2025-10-15-15-10-34.gh-issue-140166.NtxRez.rst
new file mode 100644
index 00000000000000..c140db9dcd5150
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-10-15-15-10-34.gh-issue-140166.NtxRez.rst
@@ -0,0 +1 @@
+:mod:`mimetypes`: Per the `IANA assignment <https://www.iana.org/assignments/media-types/application/texinfo>`_, update the MIME type for the ``.texi`` and ``.texinfo`` file formats to ``application/texinfo``, instead of ``application/x-texinfo``.