Chinese shrimp, , is widely cultured in China for its high economic value. However, farming yields of F. chinensis have decreased in the past few decades. The decreases in yield has been attributed to disease, as environmental deterioration due to poor management has resulted in an increased incidence of stress-induced disease. Environmental stressors, such as ammonia, have a significant effect on the antioxidant system of shrimp. However, little information is available about the effects of changes in ambient ammonia-N on hemolymph nitrogen content and antioxidant capability of Chinese shrimp. Therefore, 600 shrimps[initial body weight, (5.0±1.2) g] were divided randomly into five groups and exposed to water containing different concentrations of ambient ammonia-N (0 mg/L, 2 mg/L, 4 mg/L, 6 mg/L, and 8 mg/L). Each group had six replicates of 20 shrimp each. Total antioxidant capacity (T-AOC), antisuperoxide anions, relative expression of catalase (), and caspase mRNA in hemocytes and hemolymph ammonia, and urea content were analyzed in hemolymph after exposing shrimp to different concentrations of ambient ammonia-N for 6 h, 24 h, 48 h, 72 h, and 96 h. Shrimp cultured in filtered seawater were used as the control. The results showed that ammonia accumulated gradually in the hemolymph as exposure time increased. Hemolymph ammonia content of shrimp in the 8 mg/L group was the highest compared with that in the other groups and was 5.85 times higher than that in the control group. Hemolymph urea contents of shrimp in the ammonia-N exposed groups were higher than that in the control group after 6 h of am-monia-N exposure. The hemolymph urea of shrimp in the 6 mg/L group was the highest after 6 h and was 2.22-times higher than that in the control group. Hemolymph T-AOC and mRNA expression in hemocytes of shrimp exposed to ambient ammonia-N increased initially and then decreased as exposure time increased. However, anti-superoxide anions in hemolymph and relative mRNA expression levels in hemocytes increased, decreased, and then increased again as exposure time increased. The antioxidant capacity of shrimp was significantly higher after exposure to ammonia-N than that in the control. These findings demonstrate that the oxidation-antioxidant balance system in shrimp may be damaged after exposure to ammonia-N, resulting in upregulation of caspase mRNA expression.