Xenotransplantation with porcine organs has been recognized as a promising solution to alleviate the shortage of organs for human transplantation. Porcine endogenous retrovirus (PERV), whose proviral DNAs are buried in the genome of all pig breeds, is a main microbiological risk for xenotransplantation. Over the last decades, some advances on PERVs’ study have been achieved. Here we reviewed the current progress of PERVs including the classification, molecular structure, regulation , function in immune system and potential risk in xenotransplantation. We also discussed the problem of insufficient research on PERVs as well as the questions need to be answered in the future work.