Live AMERVAC PRRS vaccine produced by HIPRA Laboratory, SA (Spain),was used for testing on pigs raising in Vietnam. The tested result indicated that this vaccine was safe in use. Vaccine virus did not transmit horizontally from experimental pigs to control pigs and had the effect in inducing immune response at higher level when the pig was infected with challenge virus. Immune response induced by vaccine had the effect in reducing the serious level of disease when challenge with 2 virus strains of Vietnam. This result showed clearly when testing the gross and histobiologicallesions in internal organs (particularly is lung). The vaccinated pigs also increased higher body weight compared to the control pigs when applying challenge test. Immune response induced by vaccinating AMERVAC PRRS vaccine had removed the entire of virus in pigs in 2-3 weeks after pigs were infected with PRRS.