diff --git a/.changeset/shaggy-toes-speak.md b/.changeset/shaggy-toes-speak.md
new file mode 100644
index 00000000..c7c62ac0
--- /dev/null
+++ b/.changeset/shaggy-toes-speak.md
@@ -0,0 +1,5 @@
+---
+"react-mentions": patch
+---
+
+Fixed substring matching bug when typeing korean.
diff --git a/src/utils/createMatcher.js b/src/utils/createMatcher.js
new file mode 100644
index 00000000..6ec1c0ab
--- /dev/null
+++ b/src/utils/createMatcher.js
@@ -0,0 +1,51 @@
+import escapeRegex from './escapeRegex'
+
+function ch2pattern(ch) {
+  const offset = 44032 /* '가'의 코드 */
+  // 한국어 음절 (Korean syllables)
+  if (/[가-힣]/.test(ch)) {
+    const chCode = ch.charCodeAt(0) - offset
+    // 종성이 있으면 문자 그대로를 찾는다.
+    if (chCode % 28 > 0) {
+      return ch
+    }
+
+    const begin = Math.floor(chCode / 28) * 28 + offset
+    const end = begin + 27
+    return `[\\u${begin.toString(16)}-\\u${end.toString(16)}]`
+  }
+
+  // 한글 자음 (Korean consonants)
+  if (/[ㄱ-ㅎ]/.test(ch)) {
+    const con2syl = {
+      ㄱ: '가'.charCodeAt(0),
+      ㄲ: '까'.charCodeAt(0),
+      ㄴ: '나'.charCodeAt(0),
+      ㄷ: '다'.charCodeAt(0),
+      ㄸ: '따'.charCodeAt(0),
+      ㄹ: '라'.charCodeAt(0),
+      ㅁ: '마'.charCodeAt(0),
+      ㅂ: '바'.charCodeAt(0),
+      ㅃ: '빠'.charCodeAt(0),
+      ㅅ: '사'.charCodeAt(0),
+    }
+    const begin =
+      con2syl[ch] ||
+      (ch.charCodeAt(0) - 12613) /* 'ㅅ'의 코드 */ * 588 + con2syl['ㅅ']
+    const end = begin + 587
+    return `[${ch}\\u${begin.toString(16)}-\\u${end.toString(16)}]`
+  }
+
+  // 그 외엔 그대로 내보냄 (other than korean)
+  return escapeRegex(ch)
+}
+
+export default function createMatcher(input) {
+  const pattern = input
+    .split('')
+    .map(ch2pattern)
+    .map(pattern => '(' + pattern + ')')
+    .join('')
+
+  return new RegExp(pattern + '.*', 'i')
+}
diff --git a/src/utils/createMatcher.spec.js b/src/utils/createMatcher.spec.js
new file mode 100644
index 00000000..5929a656
--- /dev/null
+++ b/src/utils/createMatcher.spec.js
@@ -0,0 +1,23 @@
+import createMatcher from './createMatcher'
+
+describe('#createMatcher', () => {
+  it('should match substring including input value', () => {
+    const enRegex = createMatcher('je')
+    expect(enRegex.test('Jesse Pinkman')).toEqual(true)
+    expect(enRegex.test('Pinkman')).toEqual(false)
+
+    const enRegex2 = createMatcher('pi')
+    expect('Jesse Pinkman'.match(enRegex2).index).toEqual(6)
+    expect('Pinkman'.match(enRegex2).index).toEqual(0)
+  })
+
+  it('should match substring including Korean consonants', () => {
+    const koRegex = createMatcher('ㅅㄷ')
+    expect(koRegex.test('성덕선')).toEqual(true)
+    expect(koRegex.test('덕선')).toEqual(false)
+
+    const enRegex2 = createMatcher('ㄷㅅ')
+    expect('성덕선'.match(enRegex2).index).toEqual(1)
+    expect('덕선'.match(enRegex2).index).toEqual(0)
+  })
+})
diff --git a/src/utils/getSubstringIndex.js b/src/utils/getSubstringIndex.js
index 069d7b61..1ce4685f 100644
--- a/src/utils/getSubstringIndex.js
+++ b/src/utils/getSubstringIndex.js
@@ -1,3 +1,4 @@
+import createMatcher from './createMatcher'
 import lettersDiacritics from './diacritics'
 
 const removeAccents = str => {
@@ -16,11 +17,13 @@ const removeAccents = str => {
 export const normalizeString = str => removeAccents(str).toLowerCase()
 
 const getSubstringIndex = (str, substr, ignoreAccents) => {
-  if (!ignoreAccents) {
-    return str.toLowerCase().indexOf(substr.toLowerCase())
-  }
+  const display = ignoreAccents ? normalizeString(str) : str
+  const query = ignoreAccents ? normalizeString(substr) : substr
 
-  return normalizeString(str).indexOf(normalizeString(substr))
+  const regex = createMatcher(query)
+  const match = display.match(regex)
+
+  return match ? match.index : -1
 }
 
 export default getSubstringIndex