diff --git a/lib/maxLengthSubString.ts b/lib/maxLengthSubString.ts
new file mode 100644
index 0000000..beb6823
--- /dev/null
+++ b/lib/maxLengthSubString.ts
@@ -0,0 +1,32 @@
+export function maxLengthSubString(str: string): number {
+  const endIndex = str.length - 1;
+  let res = 1;
+  let L = 0;
+  let R = 1;
+  let subStr = str[L];
+
+  if (!str) return 0;
+  if (str.length < 2) return 1;
+
+  while (L <= endIndex && R <= endIndex) {
+    if (!subStr.includes(str[R])) {
+      subStr = subStr + str[R];
+      res = Math.max(subStr.length, res);
+      R++;
+    } else {
+      L++;
+      subStr = str[L];
+      R = L + 1;
+    }
+  }
+
+  return res;
+}
+
+console.log(maxLengthSubString("a"), "expect: " + 1);
+console.log(maxLengthSubString(""), "expect: " + 0);
+
+console.log(maxLengthSubString("abcabcbb"), "expect: " + 3);
+console.log(maxLengthSubString("ab"), "expect: " + 2);
+console.log(maxLengthSubString("aaaaaa"), "expect: " + 1);
+console.log(maxLengthSubString("aabcDfffaaaa"), "expect: " + 5);