diff --git a/src/lib/components/chat/Messages/Markdown/MarkdownInlineTokens.svelte b/src/lib/components/chat/Messages/Markdown/MarkdownInlineTokens.svelte
index 01536a7bef..a453653514 100644
--- a/src/lib/components/chat/Messages/Markdown/MarkdownInlineTokens.svelte
+++ b/src/lib/components/chat/Messages/Markdown/MarkdownInlineTokens.svelte
@@ -107,6 +107,8 @@
 		<br />
 	{:else if token.type === 'del'}
 		<del><svelte:self id={`${id}-del`} tokens={token.tokens} {onSourceClick} /></del>
+	{:else if token.type === 'underline'}
+		<u><svelte:self id={`${id}-underline`} tokens={token.tokens} {onSourceClick} /></u>
 	{:else if token.type === 'inlineKatex'}
 		{#if token.text}
 			<KatexRenderer content={token.text} displayMode={token?.displayMode ?? false} />
diff --git a/src/lib/components/common/RichTextInput.svelte b/src/lib/components/common/RichTextInput.svelte
index 53a042b6f5..2654c319fd 100644
--- a/src/lib/components/common/RichTextInput.svelte
+++ b/src/lib/components/common/RichTextInput.svelte
@@ -125,6 +125,11 @@
 		}
 	});
 
+	turndownService.addRule('underline', {
+		filter: 'u',
+		replacement: (content) => `<u>${content}</u>`
+	});
+
 	import { onMount, onDestroy, tick, getContext } from 'svelte';
 	import { createEventDispatcher } from 'svelte';
 
diff --git a/src/lib/utils/marked/extension.ts b/src/lib/utils/marked/extension.ts
index 86939c9151..c3f69faada 100644
--- a/src/lib/utils/marked/extension.ts
+++ b/src/lib/utils/marked/extension.ts
@@ -102,11 +102,30 @@ function detailsExtension() {
 	};
 }
 
+function underlineExtension() {
+	return {
+		name: 'underline',
+		level: 'inline',
+		start: (src: string) => src.indexOf('<u>'),
+		tokenizer(this: any, src: string) {
+			const match = /^<u>([\s\S]+?)<\/u>/.exec(src);
+			if (!match) return;
+
+			return {
+				type: 'underline',
+				raw: match[0],
+				text: match[1],
+				tokens: this.lexer.inlineTokens(match[1])
+			};
+		}
+	};
+}
+
 export default function (options = {}) {
 	return {
 		tokenizer: {
 			lheading: lheadingTokenizer as any
 		},
-		extensions: [detailsExtension()]
+		extensions: [detailsExtension(), underlineExtension()]
 	};
 }