Abstract: An implementation of zero-voltage transition（ZVT） semi bridgeless boost power factor correction（PFC） converter with quasi-zero-current switching（ZCS） auxiliary switch was proposed. By using an active snubber circuit, the proposed converter provides zero-voltage switching（ZVS） for the main switches and switching naturally for the boost diodes without increasing the voltage stress of them. At the same time, it also further reduces the power loss of the auxiliary switch, and realizes switching naturally for the rest of the diodes. The operating modes of the converter were analyzed theoretically, the constraints under soft switching and control strategy design for the converter were discussed in detail. On the basis of it, the parameters of the active snubber were given. A prototype of proposed circuit operating at 100 k Hz switching frequency, 400 V/600 W rated output had been built to verify the feasibility of the design scheme and the correctness of theoretical analysis.