A computer enclosure includes a cage (10), a side panel (20) and a fastening device (100). The fastening device includes a cover (40) attached to the side panel, an actuator (60), a locking member (70), and a coil spring (50). The cover includes an end plate (43) having an aperture (46) and a base (41) having a through hole (47). The actuator includes a shaft (65). The locking member includes a cantilever arm (74) and lock block (73) having a wedge (75). The actuator is slidably received in the cover with the shaft fixing the coil spring therearound and extending through the aperture. The locking member is located in the cover, the wedge is extendable into the through hole of the base. The actuator can drive the wedge upwardly and downwardly to engage with the cage for releasing and securing the side panel from and to the cage.