diff --git a/src/problem/mod.rs b/src/problem/mod.rs
index d4e1069..a5e61e1 100644
--- a/src/problem/mod.rs
+++ b/src/problem/mod.rs
@@ -138,4 +138,5 @@ mod p71_simplify_path;
 mod p155_min_stack;
 mod p150_evaluate_reverse_polish_notation;
 mod p224_basic_calculator;
-mod p21_merge_two_sorted_lists;
\ No newline at end of file
+mod p21_merge_two_sorted_lists;
+mod p104_maximum_depth_of_binary_tree;
\ No newline at end of file
diff --git a/src/problem/p104_maximum_depth_of_binary_tree.rs b/src/problem/p104_maximum_depth_of_binary_tree.rs
new file mode 100644
index 0000000..46c1a4e
--- /dev/null
+++ b/src/problem/p104_maximum_depth_of_binary_tree.rs
@@ -0,0 +1,70 @@
+/**
+ * [104] Maximum Depth of Binary Tree
+ */
+pub struct Solution {}
+
+use crate::util::tree::{to_tree, TreeNode};
+
+// 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::cell::RefCell;
+use std::collections::VecDeque;
+use std::rc::Rc;
+impl Solution {
+    pub fn max_depth(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
+        let mut queue = VecDeque::new();
+
+        let mut depth = 0;
+
+        if let Some(node) = root {
+            queue.push_back(node);
+        }        
+
+        while !queue.is_empty() {
+            let level = queue.len();
+            depth += 1;
+
+            for i in 0..level {
+                let node = queue.pop_front().unwrap();
+
+                if let Some(left) = &node.borrow().left {
+                    queue.push_back(Rc::clone(left));
+                };
+
+                if let Some(right) = &node.borrow().right {
+                    queue.push_back(Rc::clone(right));
+                };
+            }
+        }
+
+        depth
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_104() {}
+}