A heat dissipation assembly includes a printed circuit board (70) with a heat-generating device (74) mounted thereon, a heat sink (60) mounted on the heat-generating device for dissipating heat therefrom, a retaining device (1) and a locating member (50). The retaining device includes a pair of spaced pressing portions (14) pressing on the heat sink, and a pair of pivot portions (34) pivotally engaged with the pressing portions respectively. The locating member includes a baseplate (52) located at an underside of the printed circuit board, and four pins (54) extending from the baseplate. The pins pass through the printed circuit board and the heat sink. Two of the pins are engaged by the pressing portions, and the other two pins are engaged by the pivot portions when the pivot portions are pivotally moved toward the printed circuit board.