Abstract: An air duct of a radiating fan having an air duct body and guide plates installed within the air duct body. A plurality of positioning holes with special arrangement are installed on the periphery of the wind outlet of air duct body. The front and rear sides of the guide plate are installed with pivotal pins. Thereby, the guide plate can be buckled to respective positioning holes so to form different angles with the air duct body. Therefore, the orientation and size of the channel of air flow is changed. As consequence, the guide plates can be installed on the wind outlet of the radiating fan of an electronic device and the airflow actually attains the predetermined place and the heat dissipating efficiency is increased.