diff --git a/Lib/mimetypes.py b/Lib/mimetypes.py
--- a/Lib/mimetypes.py
+++ b/Lib/mimetypes.py
@@ -381,22 +381,24 @@ def _default_mime_types():
     global types_map
     global common_types
 
     suffix_map = {
         '.tgz': '.tar.gz',
         '.taz': '.tar.gz',
         '.tz': '.tar.gz',
         '.tbz2': '.tar.bz2',
+        '.txz': '.tar.xz',
         }
 
     encodings_map = {
         '.gz': 'gzip',
         '.Z': 'compress',
         '.bz2': 'bzip2',
+        '.xz': 'xz',
         }
 
     # Before adding new types, make sure they are either registered with IANA,
     # at http://www.isi.edu/in-notes/iana/assignments/media-types
     # or extensions, i.e. using the x- prefix
 
     # If you add to these, please keep them sorted!
     types_map = {
diff --git a/Lib/test/test_mimetypes.py b/Lib/test/test_mimetypes.py
--- a/Lib/test/test_mimetypes.py
+++ b/Lib/test/test_mimetypes.py
@@ -16,16 +16,18 @@ class MimeTypesTestCase(unittest.TestCas
         self.db = mimetypes.MimeTypes()
 
     def test_default_data(self):
         eq = self.assertEqual
         eq(self.db.guess_type("foo.html"), ("text/html", None))
         eq(self.db.guess_type("foo.tgz"), ("application/x-tar", "gzip"))
         eq(self.db.guess_type("foo.tar.gz"), ("application/x-tar", "gzip"))
         eq(self.db.guess_type("foo.tar.Z"), ("application/x-tar", "compress"))
+        eq(self.db.guess_type("foo.tar.bz2"), ("application/x-tar", "bzip2"))
+        eq(self.db.guess_type("foo.tar.xz"), ("application/x-tar", "xz"))
 
     def test_data_urls(self):
         eq = self.assertEqual
         guess_type = self.db.guess_type
         eq(guess_type("data:,thisIsTextPlain"), ("text/plain", None))
         eq(guess_type("data:;base64,thisIsTextPlain"), ("text/plain", None))
         eq(guess_type("data:text/x-foo,thisIsTextXFoo"), ("text/x-foo", None))