Abstract: To study the immune modulating mechanism of Rice Bran Polysaccharide (RBS) on immunosuppressed chick, the flow cytometry technique was used to detect the DNA content, cell cycle and apoptosis rate of spleen and bursa cells of chickens in healthy, and immunosuppressed chicks induced by CTX and IBDV under the conditions of giving and not giving with RBS at dosage of 150 mg/(kg·d) by intragastric administration. The results were as follows: 1) The cell ratio of S phase and proliferation index (PI) in spleen of CTX+RBS group were higher than that of CTX group (P< 005), whereas there was no significant difference of bursa cell cycle between CTX+RBS and CTX group (P>005). 2) The cell ratio of S and G2 phase and the PI in spleen and the cell ratio of S phase and the PI in bursa of IBDV+RBS group were higher than that of IBDV group (P<005). 3) The apoptosis rate of spleen and bursa in CTX+RBS and IBDV+RBS group were lower respectively than that of CTX and IBDV group (P<005). These data indicated that the RBS could improve DNA replication of spleen cells in chickens treated with CTX, as well as spleen and bursa cells in chickens artificially infected by IBDV, and that the RBS could inhibit the apoptosis of spleen and bursa cells in chickens treated with CTX and IBDV.