The Pacific white shrimp, Litopenaeus vannamei, originated in Pacific coastal waters but are now widely farmed in inland China and are one of the most important farmed aquatic species world-wide. Leucine plays an important role in the maintenance of nitrogen balance, energy metabolism, blood glucose concentration, growth hormone and hemoglobin concentration, and also stimulates protein synthesis in muscle tissues. Thus, a deficiency of leucine in diets can cause severe biochemical malfunction, including growth retardation. Until now however, the optimal leucine requirements of white shrimp were unknown. We evaluated the leucine requirements of juvenile Pacific white shrimp Litopenaeus vannamei (Boone) in low-salinity water(0.6−0.8 g/L). Six diets containing fish meal, peanut meal and crystalline amino acids with different concentrations of L-leucine(15.95, 17.95, 19.95, 21.95, 23.95, and 25.95 g/kg dry diet) were formulated to contain 400 g/kg crude protein. A total of 1 000 healthy shrimps (initial body weight: 0.38±0.004 g) were randomly distributed into 18 rectangular fiberglass aquariums (280 L, 3 aquaria per diet, 30 shrimps per aquarium) and fed one of the diets for 56 d. Weight gain rate increased significantly with increasing leucine concentration up to 23.95 g/kg dietary leucine (diet L11, P<0.05). The diets containing higher leucine concentrations had no effect on growth performance (P>0.05). Group L11 had the highest protein efficiency ratio (PER), body protein deposition (BPD), hemolymph total protein (TP), and the lowest feed conversion ratio (FCR), hemolymph aspartate aminotransferase (AST), alanine transaminase (ALT) activities, and hemolymph urea nitrogen (HUN) content. The PER, BPD, and TP of group L11 were significantly higher than those of group L7, whereas the FCR, AST, ALT, and HUN of group L11 were significantly lower than those of group L7(P<0.05). The survival of group L7 was lower than that of group L9 and L10 (P<0.05), but there was no significant difference among the other groups(P>0.05). Our results suggest that a lack of dietary leucine decreases growth performance and survival of Pacific white shrimp. A broken-line regression calculated using weight gain rate indicated that the optimal dietary leucine requirement for L. vannamei reared in low-salinity water was 24.80 g/kg leucine of dry diet, corresponding to 61.99 g/kg leucine of dietary protein.