The feasibility of Laminaria japonica powder (LJP) combined with cecropin as a dietary supplement to enhance broiler growth performance and immune function was evaluated in this study. In total, 648 oneday-old Arbor Acres broiler chicks were randomly distributed into nine numerically-equal treatment groups: T 1 (control group; fed a basal diet); T 2 (fed the basal diet supplemented with 1% LJP);T 3 (fed the basal diet supplemented with 300mg cecropin/kg); and T 4 ,T 5 ,T 6 ,T 7 ,T 8 and T 9 , individually fed with the dietary supplemented with varying levels of LJP and cecropin). Compared with the control, dietary of LJP or cecropin supplementation slightly improved feed conversion ratio (FCR). However, the dietary supplementation of LJP combined with cecropin significantly improved broiler growth performance during the periods of 1-21,21-42, and 1-42 days (p<0.05).The dietary supplementation of 3% LJP combined with 300 mg/kg cecropin significantly increased FCR, and serum Newcastle disease antibody titers and lymphocyte numbers during the periods of 1-21, 21-42, and 1-42 days (p<0.05). Cecal microorganisms were cultivated and the number of Escherichia coli and Lactobacillus colonies were counted. The dietary supplementation of LJP combined with cecropin remarkably inhibited E. coli growth and increased Lactobacillus growth. The results of this study demonstrate the feasibility of using LJP and cecropin as feed supplement for improving the growth performance and enhancing the immune function of broilers.