In this study, the polypeptide powder of Aronia melanocarpa was taken as the research object for investigating its in vitro antioxidant function and its effect on the immune function of mice. By measuring the transformation of spleen lymphocytes, delayed-type hypersensitivity, serum hemolysin and other indicators of mice, it was found that compared with the negative control group, the high-dose group had significantly increased delayed-type hypersensitivity (P=0.009), antibody-producing ability (P=0.046), serum hemolysin level (P=0.040), carbon clearance ability (P=0.001) and NK cell activity (P=0.018); the medium-dose significantly enhanced the proliferation ability of spleen lymphocytes in mice (P=0.038); the low-dose could enhance the carbon clearance ability in mice (P=0.042); Secondly, through the analyses using the DPPH free radical assay, and hydroxyl radical and superoxide anion radical kits, it was found that the half-scavenging concentrations, IC50 values were 0.07 mg/mL, 13.91 mg/mL, and 10.00 mg/mL, respectively, and the total antioxidant capacity was 72.76 U/mL. The scavenging rates for DPPH free radicals, hydroxyl radicals, and superoxide anion free radicals were all dose-dependent with the concentration of berry polypeptide. The research results showed that the polypeptide powder of Aronia melanocarpa not only can enhance the immune function