A heat sink mounting assembly includes a socket (90) having first and second side, a retaining clip (10) cooperating with the socket to sandwich a heat sink (70) therebetween. A pair of ears (92) is formed at the first and second sides of the socket. The retaining clip includes a pressing body (11) having first and second ends, a first leg (14) extending from the first end thereof and engaging with one ear, a spring (50) attached to the pressing body, and a second leg (30) attached to the second end thereof and biased by the spring. When the second leg is pressed down toward the socket, the spring biases the second leg upwardly, so that the second leg is resiliently engaged with the other ear. Thus, the heat sink is secured between the socket and the retaining clip.