A heat dissipation assembly includes a heat sink (100), a fan (200) and a fan holder (300). The heat sink includes a plurality of fins (110) and defines a groove (122) in the fins at a base end thereof. The holder includes a bracket (310). The fan is secured to a first main side of the bracket. A locating flange (352) is formed adjoining an edge of a second main side opposite to the first main side of the bracket. A pair of locking flanges (362) is formed adjoining opposite edges of the second main side of the bracket, disposed at opposite sides of the locating flange. The locating and locking flanges are received in the groove of the heat sink and abuttingly engaged with an inner defined at the heat sink in the groove. The base end of the heat sink is received between the bracket and the flanges.