diff --git a/components/Sidebar/MermaidDiagram.tsx b/components/Sidebar/MermaidDiagram.tsx
new file mode 100644
index 00000000..785ae005
--- /dev/null
+++ b/components/Sidebar/MermaidDiagram.tsx
@@ -0,0 +1,97 @@
+import React, { useEffect, useRef, useState } from 'react'
+import { Box } from '@chakra-ui/react'
+
+let mermaidId = 0
+let mermaidLoaded: Promise<any> | null = null
+
+function loadMermaid(): Promise<any> {
+  if (mermaidLoaded) return mermaidLoaded
+  mermaidLoaded = new Promise((resolve, reject) => {
+    if (typeof window !== 'undefined' && (window as any).mermaid) {
+      resolve((window as any).mermaid)
+      return
+    }
+    const script = document.createElement('script')
+    script.src = 'https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.min.js'
+    script.onload = () => {
+      const m = (window as any).mermaid
+      m.initialize({ startOnLoad: false, theme: 'dark', securityLevel: 'loose' })
+      resolve(m)
+    }
+    script.onerror = reject
+    document.head.appendChild(script)
+  })
+  return mermaidLoaded
+}
+
+export interface MermaidDiagramProps {
+  code: string
+}
+
+export const MermaidDiagram = ({ code }: MermaidDiagramProps) => {
+  const [svg, setSvg] = useState<string>('')
+  const [error, setError] = useState<string>('')
+  const [id] = useState(() => `mermaid-${mermaidId++}`)
+
+  useEffect(() => {
+    let cancelled = false
+    loadMermaid()
+      .then(async (mermaid) => {
+        try {
+          const { svg: rendered } = await mermaid.render(id, code)
+          if (!cancelled) {
+            setSvg(rendered)
+            setError('')
+          }
+        } catch (e: any) {
+          if (!cancelled) {
+            setError(e?.message || 'Failed to render diagram')
+            setSvg('')
+          }
+        }
+      })
+      .catch((e: any) => {
+        if (!cancelled) {
+          setError('Failed to load Mermaid library')
+        }
+      })
+    return () => {
+      cancelled = true
+    }
+  }, [code, id])
+
+  if (error) {
+    return (
+      <Box
+        p={3}
+        my={3}
+        bg="red.900"
+        color="red.200"
+        borderRadius="md"
+        fontFamily="monospace"
+        fontSize="sm"
+      >
+        Mermaid error: {error}
+      </Box>
+    )
+  }
+
+  if (!svg) {
+    return (
+      <Box p={3} my={3} color="gray.400" fontSize="sm">
+        Rendering diagram...
+      </Box>
+    )
+  }
+
+  return (
+    <Box
+      my={3}
+      p={2}
+      borderRadius="md"
+      overflow="auto"
+      sx={{ '& svg': { maxWidth: '100%' } }}
+      dangerouslySetInnerHTML={{ __html: svg }}
+    />
+  )
+}
diff --git a/util/processOrg.tsx b/util/processOrg.tsx
index 2abc256a..2520b129 100644
--- a/util/processOrg.tsx
+++ b/util/processOrg.tsx
@@ -30,6 +30,7 @@ import { LinksByNodeId, NodeByCite, NodeById } from '../pages'
 import React, { createContext, ReactNode, useMemo } from 'react'
 import { OrgImage } from '../components/Sidebar/OrgImage'
 import { Section } from '../components/Sidebar/Section'
+import { MermaidDiagram } from '../components/Sidebar/MermaidDiagram'
 import { NoteContext } from './NoteContext'
 import { OrgRoamLink, OrgRoamNode } from '../api'
 
@@ -168,6 +169,40 @@ export const ProcessedOrg = (props: ProcessedOrgProps) => {
             img: ({ src }) => {
               return <OrgImage src={src as string} file={previewNode?.file} />
             },
+            pre: ({ children, className }) => {
+              // Detect mermaid code blocks: uniorg emits <pre class="src src-mermaid">
+              // and remark emits <pre><code class="language-mermaid">
+              const classStr = String(className || '')
+
+              // Extract text content from React children recursively
+              const extractText = (node: any): string => {
+                if (!node) return ''
+                if (typeof node === 'string') return node
+                if (typeof node === 'number') return String(node)
+                if (Array.isArray(node)) return node.map(extractText).join('')
+                if (node?.props?.children) return extractText(node.props.children)
+                return ''
+              }
+
+              // Check for org-mode: <pre class="src src-mermaid">
+              if (classStr.includes('src-mermaid')) {
+                const code = extractText(children).trim()
+                if (code) return <MermaidDiagram code={code} />
+              }
+
+              // Check for markdown: <pre><code class="language-mermaid">
+              const childArray = children ? React.Children.toArray(children as ReactNode) : []
+              if (childArray.length === 1 && React.isValidElement(childArray[0])) {
+                const codeEl = childArray[0] as React.ReactElement<any>
+                const codeClass = String(codeEl.props?.className || '')
+                if (codeClass.includes('language-mermaid')) {
+                  const code = extractText(codeEl).trim()
+                  if (code) return <MermaidDiagram code={code} />
+                }
+              }
+
+              return <pre className={classStr || undefined}>{children as ReactNode}</pre>
+            },
             section: ({ children, className }) => {
               if (className && (className as string).slice(-1) === `${previewNode.level}`) {
                 return <Box>{(children as React.ReactElement[]).slice(1)}</Box>