diff --git a/python/number_of_closed_islands.py b/python/number_of_closed_islands.py
new file mode 100644
index 0000000..88944ab
--- /dev/null
+++ b/python/number_of_closed_islands.py
@@ -0,0 +1,30 @@
+# https://leetcode.com/problems/number-of-closed-islands/description/
+# T: O(m*n) 
+# S: O(m*n) 
+
+class Solution:
+    def closedIsland(self, grid: List[List[int]]) -> int:
+        m = len(grid)
+        n = len(grid[0])
+        visit = [[False] * n for _ in range(m)]
+        count = 0
+
+        def dfs(x: int, y: int, m: int, n: int, grid: List[List[int]], visit: List[List[bool]]) -> bool:
+            if x < 0 or x >= m or y < 0 or y >= n:
+                # (x, y) is a boundary cell.
+                return False
+            if grid[x][y] == 1 or visit[x][y]:
+                # (x, y) is not a valid cell to visit.
+                return True
+            visit[x][y] = True
+            isClosed = True
+            for dx, dy in [(0, 1), (1, 0), (0, -1), (-1, 0)]:
+                isClosed &= dfs(x + dx, y + dy, m, n, grid, visit)
+            return isClosed
+
+        for i in range(m):
+            for j in range(n):
+                if grid[i][j] == 0 and not visit[i][j] and dfs(i, j, m, n, grid, visit):
+                    count += 1
+
+        return count