diff --git a/src/problem/mod.rs b/src/problem/mod.rs
index 776eed3..ca81fb6 100644
--- a/src/problem/mod.rs
+++ b/src/problem/mod.rs
@@ -44,4 +44,5 @@ mod p2641_cousins_in_binary_tree_ii;
 mod p993_cousins_in_binary_tree;
 mod p236_lowest_common_ancestor_of_a_binary_tree;
 mod p94_binary_tree_inorder_traversal;
-mod p144_binary_tree_preorder_traversal;
\ No newline at end of file
+mod p144_binary_tree_preorder_traversal;
+mod p145_binary_tree_postorder_traversal;
\ No newline at end of file
diff --git a/src/problem/p145_binary_tree_postorder_traversal.rs b/src/problem/p145_binary_tree_postorder_traversal.rs
new file mode 100644
index 0000000..4dad7da
--- /dev/null
+++ b/src/problem/p145_binary_tree_postorder_traversal.rs
@@ -0,0 +1,75 @@
+/**
+ * [145] Binary Tree Postorder Traversal
+ */
+pub struct Solution {}
+
+use crate::util::tree::{TreeNode, to_tree};
+
+// submission codes start here
+
+// Definition for a binary tree node.
+// #[derive(Debug, PartialEq, Eq)]
+// pub struct TreeNode {
+//   pub val: i32,
+//   pub left: Option<Rc<RefCell<TreeNode>>>,
+//   pub right: Option<Rc<RefCell<TreeNode>>>,
+// }
+//
+// impl TreeNode {
+//   #[inline]
+//   pub fn new(val: i32) -> Self {
+//     TreeNode {
+//       val,
+//       left: None,
+//       right: None
+//     }
+//   }
+// }
+use std::rc::Rc;
+use std::cell::RefCell;
+impl Solution {
+    pub fn postorder_traversal(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<i32> {
+        let mut result = Vec::new();
+        let mut stack = Vec::new();
+        let mut root = root;
+        let mut prev = None;
+
+        while root.is_some() || !stack.is_empty() {
+            while let Some(r) = root {
+                stack.push(Rc::clone(&r));
+                root = r.borrow().left.clone();
+            }
+
+            root = stack.pop();
+            if let Some(r) = root {
+                if r.borrow().right.is_none() || r.borrow().right == prev {
+                    result.push(r.borrow().val);
+                    prev = Some(r);
+                    root = None;
+                } else {
+                    stack.push(Rc::clone(&r));
+                    root = r.borrow().right.clone();
+                }
+            }
+        }
+
+        result
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_145() {
+        assert_eq!(Solution::postorder_traversal(
+            to_tree(vec![Some(1), None, Some(2), Some(3)])),
+                   vec![3,2,1]);
+        assert_eq!(Solution::postorder_traversal(
+            to_tree(vec![Some(2), None, Some(3), None, Some(1)])
+        ), vec![1,3,2]);
+    }
+}