diff --git a/Lib/base64.py b/Lib/base64.py
index fa562f74a81034..dd4475c40c8f19 100644
--- a/Lib/base64.py
+++ b/Lib/base64.py
@@ -462,31 +462,31 @@ def decodebytes(s):
 # Usable as a script...
 def main():
     """Small main program"""
-    import sys, getopt
-    usage = f"""usage: {sys.argv[0]} [-h|-d|-e|-u] [file|-]
-        -h: print this help message and exit
-        -d, -u: decode
-        -e: encode (default)"""
-    try:
-        opts, args = getopt.getopt(sys.argv[1:], 'hdeu')
-    except getopt.error as msg:
-        sys.stdout = sys.stderr
-        print(msg)
-        print(usage)
-        sys.exit(2)
-    func = encode
-    for o, a in opts:
-        if o == '-e': func = encode
-        if o == '-d': func = decode
-        if o == '-u': func = decode
-        if o == '-h': print(usage); return
-    if args and args[0] != '-':
-        with open(args[0], 'rb') as f:
+    import argparse
+    import sys
+
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "-d", "-u", "--decode", action="store_true", help="decode data"
+    )
+    parser.add_argument(
+        "-e", "--encode", action="store_true", help="encode data (default)"
+    )
+    parser.add_argument("infile", nargs="?", default="-", help="the file to decode or encode")
+    args = parser.parse_args()
+    if args.decode:
+        func = decode
+    else:
+        func = encode
+
+    if args.infile != "-":
+        with open(args.infile, "rb") as f:
             func(f, sys.stdout.buffer)
     else:
         if sys.stdin.isatty():
             # gh-138775: read terminal input data all at once to detect EOF
             import io
+
             data = sys.stdin.buffer.read()
             buffer = io.BytesIO(data)
         else:
diff --git a/Lib/test/test_base64.py b/Lib/test/test_base64.py
index 868abcfee24e10..8a12d072bb9012 100644
--- a/Lib/test/test_base64.py
+++ b/Lib/test/test_base64.py
@@ -1422,8 +1422,9 @@ def get_output(self, *args):
     def test_encode_file(self):
         with open(os_helper.TESTFN, 'wb') as fp:
             fp.write(b'a\xffb\n')
-        output = self.get_output('-e', os_helper.TESTFN)
-        self.assertEqual(output.rstrip(), b'Yf9iCg==')
+        for flag in ('-e', '--encode'):
+            output = self.get_output(flag, os_helper.TESTFN)
+            self.assertEqual(output.rstrip(), b'Yf9iCg==')
 
     def test_encode_from_stdin(self):
         with script_helper.spawn_python('-m', 'base64', '-e') as proc:
@@ -1434,18 +1435,20 @@ def test_encode_from_stdin(self):
     def test_decode(self):
         with open(os_helper.TESTFN, 'wb') as fp:
             fp.write(b'Yf9iCg==')
-        output = self.get_output('-d', os_helper.TESTFN)
-        self.assertEqual(output.rstrip(), b'a\xffb')
+        for flag in ('-d', '--decode'):
+            output = self.get_output(flag, os_helper.TESTFN)
+            self.assertEqual(output.rstrip(), b'a\xffb')
 
     def test_prints_usage_with_help_flag(self):
-        output = self.get_output('-h')
-        self.assertIn(b'usage: ', output)
-        self.assertIn(b'-d, -u: decode', output)
+        for flag in ('-h', '--help'):
+            output = self.get_output(flag)
+            self.assertIn(b'usage: ', output)
+            self.assertIn(b'-d', output)
 
     def test_prints_usage_with_invalid_flag(self):
         output = script_helper.assert_python_failure('-m', 'base64', '-x').err
         self.assertIn(b'usage: ', output)
-        self.assertIn(b'-d, -u: decode', output)
+        self.assertIn(b'-d', output)
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/Misc/NEWS.d/next/Library/2026-06-25-14-05-32.gh-issue-152150.lKgHxY.rst b/Misc/NEWS.d/next/Library/2026-06-25-14-05-32.gh-issue-152150.lKgHxY.rst
new file mode 100644
index 00000000000000..f331de51144d03
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-06-25-14-05-32.gh-issue-152150.lKgHxY.rst
@@ -0,0 +1,2 @@
+:mod:`base64`: Replace :mod:`getopt` with :mod:`argparse` for parsing
+command line arguments.