As far as the authors knew, there were limited studies evaluating the effects of antibacterial peptide on the serum cytokines.The aim of this study was to investigate the effects of dietary antimicrobial peptide (ABP) supplementation on contents of serum IL-2, IL-4, IL-6, IFN-γ and TNF-α in weaned piglets.Ninety weaned piglets (Landrace × Yorkshire × Duroc;(21 ± 2) d of age;average weight of (8.24 ± 0.67) kg) were randomly allotted to five groups, including the control group, the antibacterial peptide groups containing 250,500 and 1 000 mg/kg antibacterial peptide, respectively, and the astragalus polysaccharide group with 400 mg/kg astragalus polysaccharide.After 5 days adaptation to dietary daidzein, the whole experimental period was 28 days.Blood samples were collected at 32,39,46, and 53 day of age.The results showed that ABP as dietary additive increased the levels of IL-2, IL-4, IL-6, IFN-γ, and TNF-α, and the effects of ABP supplementation were dose-dependent.Piglets fed with 250 mg/kg ABP had significantly higher (P <0.01 or 0.05) the level of IL-2 at 46,53 days of age, the levels of IL-4 and IL-6 at 39,46,53 days of age, the level of IFN-γ among the whole experimental period, and the level of TNF-α at 39 and 53 days of age.Supplementation with 500 mg/kg markedly increased (P < 0.01 or 0.05) the values of IL-2 and IL-4 at 39,46,53 days of age, and the values of IL-6, IFN-γ, and TNF-α among the whole experimental period.High dosage (1 000 mg/kg) of ABP supplementation significantly improved (P < 0.01)the the level of IL-4 at 39,46,53 days of age, and the values of IL-2, IL-6, IFN-γ, and TNF-α among the whole experimental period.The results indicated that dietary addition of ABP enhance the cellular and humoral immune responses of weaned piglets by improving the levels of IL-2, IL-4, IL-6, IFN-γ, and TNF-α.The optimum add dosages was found to be 1 000 mg/kg for 4-week adding.