Abstract: To investigate the effects of Water Soluble Alfalfa Polysaccharides(WSAP)on cell proliferation of broiler lymphocytes in vitro. Different concentrations of WSAP were added into cultured with ConA stimulated chicken peripheral blood, thymus, spleen lymphocytes and into cultured with LPS stimulated chicken peripheral blood, spleen, bursa of fabricius, cultured for 48 hours, use MTT colorimetric determination of lymphocyte proliferation. The results showed that(1)In this experiment, the OD values of T, B lymphocytes in a certain concentration of WSAP (4-20 μg·mL^-1)were higher than those in control groups, with the polysaccharide concentration increased, OD values increased first(1-20 μg·mL^-1)and then decreased(100-200 μg·mL^-1);(2)The same concentration WSAP on broiler peripheral blood and other immune organs, the stimulus intensity were different, peripheral blood and spleen T, B lymphocytes OD values were less than the thymus and bursa lymphocytes OD values;(3)The best stimulus concentration for peripheral blood and other organs were difference, for peripheral blood was 20 μg·mL^-1, for spleen was 8 μg·mL^-1， for bursa and thymus with 15 μg·mL^-1. In this experiment, the concentration of WSAP with 8, 15, 20 μg·mL^-1 could promote the broiler lymphocyte proliferation, which may be the one of the mechanisms that polysaccharides could enhance immune function.