This experiment was conducted to investigate the effects of antibacterial pepitides (cecropin, ABPs) on growth performance, immune organ indices and mRNA expression levels of proinflammatory cytokine genes in jejunum of Hy-Line Brown young roosters for egg production. Three hundred and thirty-six 1-day-old healthy Hy-Line Brown young roosters for egg production were selected, and randomly divided into seven groups with four replicates in each group and twelve chicks in each replicate. The young roosters in seven groups were fed a basal diet (control group), basal diet+150 mg/kg aureomycin (antibiotics group), and basal diet+150 (ABPs group Ⅰ), 200 (ABPs group Ⅱ), 250 (ABPs group Ⅲ), 300 (ABPs group Ⅳ), 350 mg/kg ABPs (ABPs group Ⅴ), respectively. The feeding experiment lasted for 42 days. The results showed as follows: 1) the average daily feed intake in ABPs groups Ⅲ, Ⅳ and Ⅴ were significantly lower than that in the control group (P<0.05), and the F/G in ABPs groups Ⅳ and Ⅴ was significantly lower than that in the control group(P<0.05), but there was no significant difference in average daily gain among all groups (P>0.05). 2) The thymus index in ABPs group Ⅴ was significantly higher than that in the other groups (P<0.05), and the bursa of Fabricius index was significantly higher than that in the control group and ABPs group Ⅰ (P<0.05);there was no significant difference in the spleen index between ABPs group Ⅳ and ABPs group Ⅴ (P>0.05), but ABPs group Ⅴ was significantly higher than the other groups (P<0.05). 3) The relative expression level of IL-6 gene in ABPs group Ⅴ was significantly decreased compared with that in the other groups (P<0.05), that of IFN-γ gene in ABPs groups Ⅲ, Ⅳ and Ⅴ was significantly lower than that in the control group (P<0.05), and that of TNF-α gene in ABPs groups Ⅳ and Ⅴ was significantly lower than that in the control group (P<0.05). To sum up, ABPs added in the basal diet can improve growth performance and immune function, and decrease mRNA relative expression level of cytokine genes in jejunum of young roosters for egg production to some extent. The optimal added amount is 350 mg/kg.