A variable gain amplifier (VGA) circuit and an automatic gain control (AGC) method thereof are disclosed. The VGA circuit includes an amplifier circuit and an AGC circuit. The amplifier circuit amplifies an input signal to an output signal according to a predetermined gain and the AGC circuit is connected to the amplifier circuit for regulating the predetermined gain. The AGC circuit further includes a peak detector detecting a peak of the output signal, a replica of the peak detector for detecting a peak of a reference signal, and a comparator for comparing the peak of the output signal with the peak of the reference signal to provide a control signal and then providing the control signal to the amplifier circuit to regulate the predetermined gain.