A hard disk assembly includes a tray, a bracket, and a carrier. The tray includes plural protrusions. The bracket is disposed on the tray for fastening a hard disk device. The bracket includes a bracket body having plural slots thereon, and plural pins disposed on opposite sides of the bracket body. The slots are respectively engaged with the protrusions. The pins are disposed between the bracket and the tray. The carrier is pivotally connected to the tray. The carrier includes two ribs. Each rib has a curved surface for touching and pulling the pins. Therefore the bracket can be slidably moved on the tray along the slots.