A hard disk tray adapted for accommodating a hard disk having a plurality of screw holes at two sides is provided. The hard disk tray includes a body and a cover. The body includes two body lateral walls and a plurality of fixing members protruding from the two body lateral walls and corresponding to at least a part of the screw holes. The cover is pivoted to the body and includes two cover lateral walls. When the hard disk is placed in the hard disk tray, the fixing members extend into the at least a part of the screw holes, and when the cover is closed to the body, the two cover lateral walls are located outside the two body lateral walls so as to prevent the two body lateral walls from moving outwardly. A hard disk rack assembly is further provided.