diff --git a/LongestSubstringWoRepeatingCharacters.py b/LongestSubstringWoRepeatingCharacters.py
new file mode 100644
index 0000000..aceb823
--- /dev/null
+++ b/LongestSubstringWoRepeatingCharacters.py
@@ -0,0 +1,15 @@
+class Solution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
+        n = len(s)
+        unique_list = []
+        res = 0
+        for i in range(n):
+            for j in range(i, n):
+                if(s[j] in unique_list):
+                    unique_list.clear()
+                    break
+                else:
+                    unique_list.append(s[j])
+                    if(res < j - i + 1):
+                        res = j - i + 1
+        return res