A computer enclosure includes an airflow guide (10), a chassis (20) for mounting the airflow guide therein, a fan 30 mounted in the airflow guide, and a side panel (27) for covering the chassis. The chassis includes a rear panel (25) and a motherboard (21) mounted therein, a heat sink (23) is mounted on the motherboard, a plurality of openings (253) for dissipating heat and a fixing slot (251) are defined in the rear panel. The fan aligns with an area of the openings of the rear panel. The airflow guide encases the heat sink therein and includes a catch (1371) engaging in the fixing slot of the chassis. The side panel covers the chassis and abuts against the airflow guide for preventing the catch disengaging from the fixing slot.