In order to study the effects of two polysaccharides on specific-humoral immunity and T subpopulations in piglets pheripheral blood in the immune response to PRRSV killed virus vaccine, 24 35-day-old piglets were randomly assigned into equal six groups and five groups were vaccinated with PRRSV killed virus vaccine. At the same time, the piglets in groups 1 to 4 were intramuscularly injected with Chinese yam polysaccharide(CYPS) at 17.10, 8.55 mg/kg, and astragalus polysaccharide(APS) at 11.50, 5.75 mg/kg, while group 5 with saline, once a day for three successive days, group 6 only injected with saline. On different time after vaccination, pheripheral blood were sampled for detection of serum antibody titer to PRRSV by ELISA and T lymphocytes subpopulations by cytofluorometry. The results showed that both polysaccharides could enhance the antibody titers, APS at high dosage was better than others and the two polysaccharides can improve the proportion of CD3+ and CD8+ lymphocytes in the piglets pheripheral blood, CYPS was better than APS. These results indicated that both polysaccharides had significant immune enhancement effect on immunity of PRRSV killed virus vaccine in piglets.