A fixing mechanism includes a chassis (400) with a plurality of fasteners (450) formed therein. A tray (100) is movably disposed in the chassis for supporting a printed circuit board (PCB) (10) which defines a plurality of apertures (13). The fasteners are relatively sliding in the apertures of the PCB respectively. The tray includes misaligned first and second driven portions (116, 138) at an end. A driving piece (200) is rotatably fixed in the chassis adjacent the end of the tray. The driving piece is generally positioned between the first and second driven portions of the tray initially, and the driving piece is rotated in a vertical plane to selectively drive the first and second driven portions to move the tray in a horizontal plane such that the fasteners clasp or unclasp the PCB.