Abstract: 150 14-day-old chickens were randomly assigned to three groups and vaccinated with ND-IB live virus vaccine. At the same time, the chickens in two experimental groups were intramuscularly injected with achyranthes bidentata polysaccharide at high and low dosages, control group were injected with physiological saline, once a day for three successive days. On day 7, 14, 21, 28, 35 and 42 after vaccination, the dynamic changes of serum Newcastle disease (ND) hemagglutination inhibition (HI) antibody titer were determined by Micromethod. On day 10, 20, 30, 40 and 50 after vaccination, blood samples from 5 chickens per group were collected to separate lymphocyte and to determine the peripheral T lymphocyte proliferation with MTT method. The content of CD4+ and CD8+ T cells were tested by using flow cytometry with doublecolorstaining method, and the weights of whole body, spleen, bursa and thymus were weighted for calculation of immune organ index. The results showed that achyranthes bidentata polysaccharide at high dosage significantly enhanced the antibody titers, promoted the proliferation of peripheral T lymphocyte, and raised the ratio of CD4+ to CD8+T lymphocyte (P < 0.05) and immune organ indexes. These results indicated that achyranthes bidentata polysaccharide had significant immune enhancement role on immunity of ND-IB vaccine in chickens.