An 8-week feeding trial was conducted to determine the dietary valine requirement of juvenile sea cucumber Apostichopus japonicus with initial body weight (9.20±0.12) g. Six experimental diets were formulated with the graded valine levels (0, 0.80%, 1.60%, 2.40%, 3.20% and 4.00% dry diets, respectively). The six trial diets were determined to contain valine of [0.61% (D1), 1.14% (D2), 1.46% (D3), 1.73% (D4), 2.17% (D5) and 2.64% (D6) dry diet], respectively. The results showed that: ① No significant differences in the survival rate (SR) were found among dietary treatments ; the weight growth rate (WGR) and the specific growth rate (SGR) increased with increasing levels of valine up to 1.73% diet, and thereafter, declined. ② There were no significant effects on ratio of intestine weight to body wall weight (IBR) and ratio of intestine length to body length (IBL) of sea cucumber. ③ Crude protein and crude lipid of body wall increased initially, then decreased, and crude protein of diet D4 was significantly higher than that of any other groups. Dietary valine significantly increased His, Val, essential amino acids (EAA) and total amino acids (TAA) contents of body wall, but decreased Leu, Ile and Tyr contents. ④ Total superoxide dismutase (T-SOD) and total antioxidant capacity (T-AOC) increased with the increasing of dietary valine levels and those of D1 were significantly lower than other groups. Malondialdehyde (MDA) content decreased with increasing levels of valine up to 1.73% diet and then increased, and MDA of D4 was significantly lower than those of other groups. ⑤ Protease and lipase increased initially and then decreased, and protease of D3 was significantly higher than that of other groups, however, there was no significantly effect on amylase of dietary valine. In conclusion, appropriate dietary valine improved significantly growth performance and immune response and modified chemical composition and amino acid contents of sea cucumbers. With WGR as evaluation indicator, regression analysis of broken-line model showed that the optimum dietary valine of sea cucumber with body weight 9.20 g was 1.79% (9.18% diet protein).