A heat dissipation device includes a heat sink (10) and a fan (30). The heat sink includes a plurality of fins (15), and a guiding portion (184) is formed in the fins. The fan is secured to the heat sink. An airflow (F) is generated by the fan for flowing through the heat sink. When the airflow meets with the guiding portion, the airflow is deflected. The deflected airflow is guided to flow across heat-generating elements.