A fan has a fan, an impeller and a motor. The impeller is disposed in the fan frame, and the motor is disposed in the fan frame for driving the impeller. The fan frame has a housing, a base and at least one connecting element. The housing has an inlet and an outlet, and the base is disposed in the housing and at the outlet. The connecting element is disposed between the housing and the base. The base has a first airflow guiding structure disposed on the circumference of the base. The housing has a second airflow guiding structure disposed on the inner circumference thereof and adjacent to the outlet. The first airflow guiding structure and the second airflow guiding structure are correspondingly disposed.