The configurations of a bridgeless PFC circuit and a controlling method thereof are provided. The proposed circuit includes an AC power source, a first and a second bridge arms, each of which has a middle point, wherein the first terminal of the first bridge arm connects the first terminal of the second bridge arm, the second terminal of the first bridge arm connects the second terminal of the second bridge arm, and the middle point of the second bridge arm connects the second terminal of the AC power source, a bidirectional switch module connected to the two middle points, an inductor having a first terminal coupled to the AC power source and a second terminal coupled to the middle point of the first bridge arm and a sensing circuit magnetically coupled to the inductor.