Abstract: A feeding trial was conducted to investigate the effects of dietary arginine on growth performance, immune responses and digestive enzyme activities of juvenile sea cucumber Apostichopus japonicus Selenka with initial body weight 9.10 g.Five experimental diets were formulated with the graded arginine levels(0, 1.00%, 2.00%, 3.00% and 4.00% dry diet, respectively).The five trial diets were determined to contain arginine of 0.32%, 0.73%, 1.16%, 1.61%, and 1.99% dry diet, respectively.Each diet was randomly assigned to triplicate groups of 30 sea cucumbers and fed once a day(16:00)for 60 days.The results showed that the weight gain rate(WGR), specific growth rate(SGR)and protein efficiency ratio(PER)were all increased by dietary arginine, and reaced maximum at D4 group;Ratio of visceral weight to body wall weight(VBR), ratio of intestine weight to body wall weight(IBR)and ratio of intestine length to body length(IBL)of D3, D4 and D5 groups were significantly lower than those of D1 and D2 groups, but there were no differences among them;Crude protein deposition of body wall was increased by dietary arginine, but there were no effects on moisture and crude lipid contents;Dietary arginine increased Glu, Arg, Leu, His, Hyp, essential amino acids(EAA)and total amino acids(TAA)contents of body wall, but decreased lysine content;Total superoxide dismutase(T-SOD), total antioxidant capacity(T-AOC), nitric oxide(NO), nitric oxide synthase(NOS), alkaline phosphataes(AKP), alanine aminotranferase(ALT)and asparate aminotransferase(AST)in coelomic fluid all increased with the increasing of dietary arginine levels(P < 0.05);There was a negative correlation between protease and dietary arginine levels(Yenzyme activity=-3.228X²Arg+2.865XArg+26.24, R²=0.934);Activities of cellulose of D3, D4 and D5 groups were significantly higher than those of D1 and D2 groups;meanwhile, activities of amylase and lipase were not affected by dietary arginine.With WGR as evaluation indicator, quadratic regression analysis showed that the optimum dietary arginine of sea cucumber with body weight 9.10 g was 1.55% of diet or 7.10% dietary crude protein.