Abstract: Molecular biological method was applied to explore the effect of biotin on mRNA expression of PCNA gene in spleen, aimed to probe the mechanism of biotin enhancing spleen cell propagation. 60 AA male broilers of 1 day were allocated into 3 treatments, 20 broilers per treatment. The basal diet was wheat-caseinfish meal diet. Biotin was added in the basal diet at 0.3 mg/kg and 2.7 mg/kg. There were 3 diets including the control of basal diet. In order to stimulate mRNA expression of PCNA gene, The avian flu vaccine was injected quantificationally and hypodermically into broilers on day 48. The results showed that addition of biotin elevated significantly mRNA expression level of PCNA gene in spleen (P<0.01), The mRNA expression level of 2.7 mg/kg treatment was higher significantly than that of the control and 0.3 mg/kg treatment (P<0.01), and no significant difference was founded between 0.3 mg/kg treatments and the control group.(P>0.05). It was concluded that biotin can elevate mRNA expression level of PCNA gene, thus enhance the propagation of spleen cell.