The virus neutralization test (VNT) in cell culture allows the quantitation of antibodies in pig serum that neutralize the PRRS viruses from different origins, preliminarily evaluates the protective immunity. In this study, the authors established the method of PRRS virus neutralization in Marc145 cells, in the first steps evaluated the antibody titers in apparently normal pigs comparing the results with those using ELISA and IPMA. Different from the ELISA and IPMA results, the VN ones were obtained as positive only when the Vietnamese PRRS viruses were used but not with the America or Europe origin viruses. As a conclusion, the VNT could be used to measure the immune answer of pigs towards the local viruses.