Objective To explore the influence of yeast polysaccharides (YPS)on immune system of chicken. Methods YPS were given per stomach(20mg/kg)or intramuscularly (2mg/kg) in order to study the effect on spleen,Fabricicus' bursa and T-lymphocyte of chicken. Results The results showed that the gains in weight of spleen,bursa folds and the number of T-lymphocyte were higher in study groups than in control group. Conclusion YPS can improve immunologic function of chicken, showing its potential application in poultry breeding.