Abstract: To explore the effects of different dietary vitamin C（VC） levels on immune fuctions of layer，240 forty-five-day-old Roman brown eggshell layers were randomly allocated to five groups(A,B，C，D，E) with 48 layers for each group which had 4 replicates(12 layers per cage). A group was control and B，C，D，E groups were injected with I series of Newcastle disease vaccine in subcutaneous.The basic diet with VC levels of 0，250，500，750 mg/kg were fed to B，C，D，E groups, and the spleen，thymus，bursal’s organ index and serum HI were measured once a week.The results showed that the immune organ index of spleen and thymus in C,D,E groups which were fed with VC in diet were significantly (P<0.05) or very significantly (P<0.01) higher than B group. The bursal’s organ indexes were significantly higher than B group (P<0.05) in 21 and 28 days, and the HI antibody titer was very significantly higher than B group (P<0.01).The optimal dosage of VC in diet was 500 mg/kg(P<0.05). The results suggest that optimal dosage of VC level can promote the growth and development of layer immune organ of spleen，thymus and bursal’s organ in diet of the layers, and also significantly enhance the synthesis and secretion of antibodies in the immune system to improve the body’s immune function of layers.

Key words: vitamin C; immune organ index; layer