In an interleaved bridgeless power factor corrector and a controlling method thereof, the interleaved bridgeless power factor corrector includes an AC input power supply, two input inductors, four active components, two passive components, an output capacitor, and an output resistor, wherein the four active components are cascaded in a full bridge form to act as control switches and rectifying switches having different phases; besides, the interleaved bridgeless power factor corrector is connected to a control signal processor and a control circuit, which can output complementary switch signals to control the interleaved bridgeless power factor corrector, thereby achieving output/input ripple cancellation and frequency multiplication.