A heat dissipation device includes a heat sink, a fan holder, and a fan secured on a front side of the fan holder. The heat sink includes a base and fins on the base. An engaging groove is defined in top ends of the fins. The fan holder includes a top panel and two sidewalls extending downwardly from two lateral edges of the top panel. The top panel has an inserting protrusion at a bottom surface thereof. The two sidewalls have two latching legs at lower ends thereof. The top panel is partially placed on a front portion of the top ends of the fins, and the inserting protrusion is inserted into the engaging groove of the fins. The two sidewalls abut against two lateral sides of the heat sink, and the two latching legs fasten to two lateral sides of the base of the heat sink.