A control circuit of rotational speed of a fan is provided, wherein by a switching of a switch unit, a PWM (Pulse Wide Modulation) unit can output a sampling pulse whose period is changing. A voltage is also changing following the period after taking a sample to an AC voltage by the control unit. The voltage after sampling serves as a working voltage of a load unit, so as to enable a fan device and a lamp device of the load unit to achieve effects of adjusting speed and brightness.