A snubber circuit for decreasing a voltage spike of a buck converter includes a resistor unit, a capacitor unit, a detecting unit, and a control unit. The resistor unit provides multiple groups of resistance values. The capacitor unit provides multiple groups of capacitance values. The detecting unit detects voltage spikes of the buck converter corresponding to each group of resistance values and capacitance values. The control unit selects each group of resistance and capacitance to respectively connect to the buck converter and determines a group of resistance and capacitance corresponding to a lowest voltage spike by comparing the detected voltage spikes with each other.