diff --git a/CHANGES/1782.bugfix.rst b/CHANGES/1782.bugfix.rst
new file mode 100644
index 00000000..20ea6d5b
--- /dev/null
+++ b/CHANGES/1782.bugfix.rst
@@ -0,0 +1 @@
+Fixed ``HtmlDecoration.custom_emoji()`` to use the correct ``emoji-id`` attribute name instead of ``emoji_id`` in the ``<tg-emoji>`` tag, matching the Telegram Bot API specification.
diff --git a/aiogram/utils/text_decorations.py b/aiogram/utils/text_decorations.py
index b8edead2..c835c27b 100644
--- a/aiogram/utils/text_decorations.py
+++ b/aiogram/utils/text_decorations.py
@@ -265,7 +265,7 @@ class HtmlDecoration(TextDecoration):
         return html.escape(value, quote=False)
 
     def custom_emoji(self, value: str, custom_emoji_id: str) -> str:
-        return self._tag(self.EMOJI_TAG, value, attrs={"emoji_id": custom_emoji_id})
+        return self._tag(self.EMOJI_TAG, value, attrs={"emoji-id": custom_emoji_id})
 
     def blockquote(self, value: str) -> str:
         return self._tag(self.BLOCKQUOTE_TAG, value)
diff --git a/tests/test_utils/test_formatting.py b/tests/test_utils/test_formatting.py
index 8efc1598..25a81ba2 100644
--- a/tests/test_utils/test_formatting.py
+++ b/tests/test_utils/test_formatting.py
@@ -108,7 +108,7 @@ class TestNode:
             ],
             [
                 CustomEmoji("test", custom_emoji_id="42"),
-                '<tg-emoji emoji_id="42">test</tg-emoji>',
+                '<tg-emoji emoji-id="42">test</tg-emoji>',
             ],
             [
                 BlockQuote("test"),
diff --git a/tests/test_utils/test_text_decorations.py b/tests/test_utils/test_text_decorations.py
index 6325edb8..4ebd5f3a 100644
--- a/tests/test_utils/test_text_decorations.py
+++ b/tests/test_utils/test_text_decorations.py
@@ -59,7 +59,7 @@ class TestTextDecoration:
             [
                 html_decoration,
                 MessageEntity(type="custom_emoji", offset=0, length=5, custom_emoji_id="42"),
-                '<tg-emoji emoji_id="42">test</tg-emoji>',
+                '<tg-emoji emoji-id="42">test</tg-emoji>',
             ],
             [
                 html_decoration,