A heat dissipation device assembly includes a heat dissipation device (10) and a retaining device (20). The heat dissipation device includes a heat sink and a heat receiver (11) provided below the heat sink. The heat receiver includes an upper section (111) and a lower enlarged section (113) below the upper section. The retaining device includes a base section (22) for mounting to the upper section and pressing downwardly against the lower section. The orientation of the heat dissipation device relative to the retaining device is adjustable via a regulating structure formed between heat receiver and the retaining device.