diff --git a/swift/3-Longest-Substring-Without-Repeating-Characters.swift b/swift/3-Longest-Substring-Without-Repeating-Characters.swift
new file mode 100644
index 000000000..c175eac8d
--- /dev/null
+++ b/swift/3-Longest-Substring-Without-Repeating-Characters.swift
@@ -0,0 +1,19 @@
+class Solution {
+    func lengthOfLongestSubstring(_ s: String) -> Int {
+        guard s.count > 0 else { return 0 }
+        let list = Array(s)
+        var hs = Set<Character>()
+        var l = 0
+        var r = 0
+        var mv = 0
+        for r in 0..<s.count {
+            while hs.contains(list[r]) {
+                hs.remove(list[l])
+                l += 1
+            }
+            hs.insert(list[r])
+            mv = max(mv, r - l + 1)
+        }
+        return mv
+    }
+}