A heat dissipation assembly includes a heat sink (10), a fan (70), and a mounting device for attaching the fan to the heat sink. The mounting device includes four clips (30), and four shafts (50) pivotably connecting the clips to the heat sink. Each clip includes a main body (31), a top pressing portion (39), and a bottom mounting portion (43). A tab (45) is upwardly formed from a center of the mounting portion. Two parallel connecting portions (33) extend outwardily from two side edges of the main body respectively. The tabs of the mounting portions of the clips abut against the fan in corresponding through holes (72) thereof. The pressing pardons of the clips press an upper face of the fan at corresponding through holes thereof. Thus the fan is securely mounted on the heat sink between the pressing portion and the mounting portion of each of the clips.