An offline synchronous switching regulator is proposed for improving the efficiency thereof. Switches are coupled to switch a transformer and generate a switching signal at a secondary side of the transformer. A switching circuit is coupled to an output of the regulator to generate pulse signals in response to the switching signal and a feedback signal. Pulse signals are utilized to control a synchronous switch for rectifying and regulating the regulator. The synchronous switch includes a power-switch set and a control circuit. The control circuit receives pulse signals for turning on/off the power-switch set. The power-switch set is connected in between the transformer and the output of the regulator. A flyback switch freewheels an inductor current and can be turned on in response to the off state of the power-switch set whose on-time is correlated to the on-time of the power-switch set.