A heat dissipation device includes a base, a heat-dissipation portion attached to the base, at least one heat pipe connecting the base and the heat-dissipation portion and a fan directly secured to the heat-dissipation portion. The heat-dissipation portion comprises a square, tubular housing having opposite front and rear end portions opening to surroundings and a plurality of fins extending inclinedly and inwardly from an inner circumferential periphery of the housing. The housing of the heat-dissipation portion is employed as a fan duct to guide an airflow generated by the fan through the fins; the inclined orientation of the fins facilitates the airflow to flow toward the inner circumferential periphery of the housing and lower parts of the fins adjacent the inner circumferential periphery, whereby the airflow can effectively take heat away from the heat-dissipation portion.