A cooling fan (1) includes a fan housing (10), a stator (20), a rotor (30) and a bearing assembly (40). A tube (111) extends upwardly from a central portion of the fan housing. The stator is mounted around the tube. The bearing assembly includes a ball bearing (333) and a sleeve bearing (335) received in two ends of the tube, respectively. The rotor has a shaft (336) extending into and rotatably supported by the bearing assembly. An elastic element (332) is arranged on the ball bearing to provide a pressing force on the ball bearing toward the sleeve bearing. An oil retaining element (339) is arranged around a bottom end of the shaft and spaced from the shaft. The oil retaining element is attached to the sleeve bearing to provide oil for the sleeve bearing.