Effects of dietary carbohydrate (CBH) levels on growth, body composition, and ammonia tolerance of juvenile white shrimp Litopenaeus vannamei at a low salinity of three were evaluated. Six isonitrogenous and isolipid diets containing different CBH levels were formulated and fed to juvenile L. vannamei for 42 days in triplicate for each treatment. Weight gain and survival rate of shrimp fed 20% CBH were the greatest and differed from those fed 5% CBH and 30% CBH. Shrimp whole-body crude protein of the 20% CBH group was significantly greater than that of other treatments. Whole-body crude lipid levels increased with the increase of dietary CBH, and was significantly higher in the 20%, 25%, and 30% CBH groups than in the control. Hepatosomatic index, condition factor, whole-body moisture, and ash contents were not affected by dietary CBH levels. Hepatopancreas soluble protein peaked in shrimp fed 20% CBH, and was significantly greater than in other groups. Hepatopancreas and muscle glycogen showed a similar tendency, but peaked in shrimp fed 15% CBH. Malate dehydrogenase, pyruvate kinase, and glucose-6-phosphate dehydrogenase activities were not affected significantly by dietary CBH levels. An ammonia challenge of 96 h showed that the shrimp in the 20% CBH group had the greatest survival rate, although no significant differences were observed among treatments. This study indicates that 15%–20% dietary CBH is optimal for growth and can improve the ability of L. vannamei to handle stress at low salinities.