This experiment was conducted to investigate the effects of antimicrobial peptides on blood immune indices and intestinal microflora of 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 the seven groups were fed a basal diet (control group), the basal diet+150 mg/kg aureomycin (antibiotics group), and the 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 immunoglobulin A content in ABPs groups Ⅳ and Ⅴ was significantly higher than that in control group and antibiotics group (P<0.05), immunoglobulin G content in the other groups was significantly higher than that in control group (P<0.05), and immunoglobulin G content in ABPs groups Ⅱ, Ⅲ, Ⅳ, Ⅴ was significantly higher than that in antibiotics group (P<0.05), but there was no significant difference in immunoglobulin M content among all groups (P>0.05). 2) The complement 3 content in all ABPs groups was significantly higher than that in control group and antibiotics group (P<0.05), but there was no significant difference in complement 4 content among all groups (P>0.05). Lysozyme content in antibiotics group and ABPs groups Ⅲ, Ⅳ, Ⅴ was significantly higher than that in control group (P<0.05). 3) The number of Escherichia coli in the control group was significantly lower than that in the other groups (P<0.05), and ABPs groups Ⅲ, Ⅳ and Ⅴ was significantly lower than that in antibiotics group (P<0.05); the number of Bifidobacterium in ABPs groups Ⅱ, Ⅲ, Ⅳ and Ⅴ was significantly higher than that in control group (P<0.05); the number of Lactobacillus in ABPs groups Ⅳ and Ⅴ was significantly higher than that in control group (P<0.05); and there was no significant difference in the number of Lactobacillus between all ABPs groups and antibiotics group (P>0.05). In conclusion, adding different levels of antibacterial peptides in the diet can improve the immunity of young roosters for egg production, increase the number of Bifidobacterium and Lactobacillus of intestinal probiotics, and effectively decrease the number of Escherichia coli of pathogenic bacteria. The optimal added amount is 350 mg/kg.