diff --git a/crates/servers/storage-server/src/fs/ext4/dir.rs b/crates/servers/storage-server/src/fs/ext4/dir.rs
index c8f7ca0..254f08c 100644
--- a/crates/servers/storage-server/src/fs/ext4/dir.rs
+++ b/crates/servers/storage-server/src/fs/ext4/dir.rs
@@ -179,6 +179,25 @@ pub fn remove_entry<B: BlockDevice>(
     None
 }
 
+pub fn init_dir_block(buf: &mut [u8], self_inode: u32, parent_inode: u32, block_size: usize) {
+    for b in buf.iter_mut() { *b = 0; }
+    let mut pos = 0;
+    // "." entry
+    write_u32(buf, pos, self_inode);
+    write_u16(buf, pos + 4, 12);
+    buf[pos + 6] = 1;
+    buf[pos + 7] = 2;
+    buf[pos + 8] = b'.';
+    pos += 12;
+    // ".." entry
+    write_u32(buf, pos, parent_inode);
+    write_u16(buf, pos + 4, (block_size - 12) as u16);
+    buf[pos + 6] = 2;
+    buf[pos + 7] = 2;
+    buf[pos + 8] = b'.';
+    buf[pos + 9] = b'.';
+}
+
 pub fn list_entries<B: BlockDevice>(
     device: &mut B,
     sb: &Superblock,
diff --git a/crates/servers/storage-server/src/fs/ext4/mod.rs b/crates/servers/storage-server/src/fs/ext4/mod.rs
index 5c28a8b..338eeb3 100644
--- a/crates/servers/storage-server/src/fs/ext4/mod.rs
+++ b/crates/servers/storage-server/src/fs/ext4/mod.rs
@@ -586,5 +586,60 @@ impl<B: BlockDevice> FileSystem for Ext4<B> {
         self.open_files[handle.raw() as usize].as_ref().map(|f| f.size)
     }
 
-    fn mkdir(&mut self, _path: &[u8]) -> bool { false }
+    fn mkdir(&mut self, path: &[u8]) -> bool {
+        let (parent_inode_num, dirname) = match self.resolve_parent(path) {
+            Some(v) => v,
+            None => return false,
+        };
+        let parent_inode = match self.read_inode(parent_inode_num) {
+            Some(i) => i,
+            None => return false,
+        };
+        if !parent_inode.is_dir() { return false; }
+
+        if dir::find_entry(&mut self.device, &self.sb, self.gdt_block, &parent_inode, dirname).is_some() {
+            return false;
+        }
+
+        let new_inode_num = match self.alloc_inode() {
+            Some(n) => n,
+            None => return false,
+        };
+        let new_block = match self.alloc_block() {
+            Some(b) => b,
+            None => { self.free_inode(new_inode_num); return false; }
+        };
+
+        let mut new_inode = Self::init_empty_inode(0x4000 | 0o755);
+        new_inode.links_count = 2;
+        new_inode.size = self.sb.block_size as u64;
+        new_inode.blocks_count = (self.sb.block_size / 512) as u32;
+        if !Self::append_extent(&mut new_inode.block_data, 0, new_block as u64, 1) {
+            self.free_block(new_block);
+            self.free_inode(new_inode_num);
+            return false;
+        }
+        self.write_inode(new_inode_num, &new_inode);
+
+        let mut dir_block = [0u8; 4096];
+        dir::init_dir_block(&mut dir_block, new_inode_num, parent_inode_num, self.sb.block_size);
+        io::write_block(&mut self.device, new_block as u64, self.sb.sectors_per_block(), &dir_block);
+
+        let parent_inode = match self.read_inode(parent_inode_num) {
+            Some(i) => i,
+            None => return false,
+        };
+        if !dir::add_entry(&mut self.device, &self.sb, self.gdt_block, &parent_inode, dirname, new_inode_num, 2) {
+            self.free_block(new_block);
+            self.free_inode(new_inode_num);
+            return false;
+        }
+
+        if let Some(mut pi) = self.read_inode(parent_inode_num) {
+            pi.links_count += 1;
+            self.write_inode(parent_inode_num, &pi);
+        }
+
+        true
+    }
 }
diff --git a/crates/servers/storage-server/src/tests/ext4.rs b/crates/servers/storage-server/src/tests/ext4.rs
index 2469be5..564a2aa 100644
--- a/crates/servers/storage-server/src/tests/ext4.rs
+++ b/crates/servers/storage-server/src/tests/ext4.rs
@@ -413,6 +413,48 @@ fn create_with_missing_parent_fails() {
     assert!(fs.create(b"nodir/file.txt").is_none());
 }
 
+#[test]
+fn mkdir_creates_directory() {
+    let mut fs = Ext4::mount(format_ext4_disk()).unwrap();
+    assert!(fs.mkdir(b"subdir"));
+    let mut entries = [DirEntry::empty(); 8];
+    let count = fs.list_dir(b"/", &mut entries).unwrap();
+    assert!(entries[..count].iter().any(|e| e.name.as_bytes() == b"subdir" && e.is_dir));
+}
+
+#[test]
+fn create_file_in_subdirectory() {
+    let mut fs = Ext4::mount(format_ext4_disk()).unwrap();
+    assert!(fs.mkdir(b"docs"));
+    let h = fs.create(b"docs/readme").unwrap();
+    fs.write(h, b"content").unwrap();
+    fs.close(h);
+    let h = fs.open(b"docs/readme").unwrap();
+    let mut buf = [0u8; 32];
+    let n = fs.read(h, &mut buf).unwrap();
+    assert_eq!(&buf[..n], b"content");
+    fs.close(h);
+}
+
+#[test]
+fn list_subdirectory() {
+    let mut fs = Ext4::mount(format_ext4_disk()).unwrap();
+    assert!(fs.mkdir(b"mydir"));
+    let h1 = fs.create(b"mydir/a.txt").unwrap();
+    fs.close(h1);
+    let h2 = fs.create(b"mydir/b.txt").unwrap();
+    fs.close(h2);
+    let mut entries = [DirEntry::empty(); 8];
+    let count = fs.list_dir(b"mydir", &mut entries).unwrap();
+    assert_eq!(count, 2);
+}
+
+#[test]
+fn mkdir_nonexistent_parent_fails() {
+    let mut fs = Ext4::mount(format_ext4_disk()).unwrap();
+    assert!(!fs.mkdir(b"noparent/child"));
+}
+
 #[test]
 fn read_past_eof_returns_zero() {
     let mut fs = Ext4::mount(format_ext4_disk()).unwrap();