A computer enclosure includes a chassis (10) having bottom, side and rear panels (20, 30, 40), and first and second mounting brackets (50, 60) attached to the chassis. The bottom panel forms a rib (21). The rear panel defines a horizontal opening (42) and an engaging portion (44). Latch slots (32) are defined in the side panel. The first mounting bracket includes a vertical expansion slot (53), a bent plate (54) and a blocking tab (55). The second mounting bracket includes: a top plate (61) having latches (612) engaging in the latch slots, and catches (613) sandwiching a top edge portion of the rear panel; and a rear plate (62) having horizontal expansion slots (621), a hook (622) slidably engaging with the bent plate, a stop plate (626) abutting against the engaging portion, a stop portion (625) abutting against the rib, and a projection (624) engaging with the blocking tab.