This experiment was conducted to study the effects of Clostridium butyricum on growth performance, immune indices and the mRNA relative expression of some related cytokine genes in jejunum of egg-laying male chicks. A total of 240 one-day-old healthy Hy-Line egg-laying male chicks were randomly divided into 6 groups with 4 replicates in each group and 10 chicks in each replicate. The basal diet was supplemented with 0 (control group) and 150 mg/kg aureomycin (antibiotic group), 250 (EG250), 500 (EG500), 750 (EG750),and 1 000 mg/kg (EG1 000) Clostridium butyricum, respectively. Growth performance, immune organ indices, serum immune indices and mRNA relative expression of some related cytokines were determined in different periods. The experiment lasted for 42 days. The results showed as follows: 1) compared with the control group, average body weight and average daily gain of chicks in EG1 000 were significantly increased (P<0.05), but the supplementation of Clostridium butyricum had no effects on average daily feed intake and feed/gain ratio during the whole experimental period (P>0.05). 2) Spleen index of chicks in EG1 000 was significantly higher than that in the control group (P<0.05), but there were no significant differences in thymus index and bursa of Fabricius index of chicks among all groups (P>0.05). 3) The serum IgG content in all Clostridium butyricum groups was significantly higher than that in the control group (P<0.05), and serum IgG content in EG750 and EG1 000 was significantly higher than that in the antibiotic group (P<0.05). The serum IgA content of chicks in EG1 000 was the highest during the whole experimental period, and there was a significant difference between EG1 000 and the control group or antibiotic group (P<0.05). The serum C3 content of chicks in all Clostridium butyricum groups was significantly higher than that in the control group (P<0.05). 4) The relative expression level of IL-6 mRNA in jejunum of chicks in EG750 and EG1 000 was significantly lower than that in the control group (P<0.05); the relative expression of TNF-α mRNA in EG1 000 was the lowest during the whole experimental period, and there was a significant difference between EG1 000 and the control group (P<0.05). In conclusion, adding appropriate level of Clostridium butyricum to the diet can improve growth performance, enhance immune organ growth and function of chicks, and suppress the inflammation. The 1 000 mg/kg Clostridium butyricum had the best effect among the six groups.