, is an important mariculture species in China. Recently deteriorated pond environment due to intensive culture caused increased incidence of stress-induced diseases. It is well known that environmental stress can induce oxidative stress. However, there is little information about the effects of pH changes on antioxidant system of Chinese shrimp. In this study, Chinese shrimps were exposed to water of pH7.0 and 9.0 for 148 h and pH8.2 was set as control. T(T-AOC), anti-superoxide anion activity, catalase (CAT) activity and the expression ) gene were analyzed in gill, hepatopancreas, muscle and haemocytes of Chinese shrimp after h exposure. The T-AOC, anti-superoxide anion activity, CAT activity and the gene expression of in different tissues increased within 1214 h of pH stress. However, they were inhibited in the extending periods of pH stress time. The gene expression in heaptopancreas and muscle gradually increased, but decreased in gill and haemocytes with pH stress time prolonging. The enzyme activities and gene expression of antioxidant system in gills first reached its highest level in pH 9.0 group, faster than other tissues in 9.0 group. And the antioxidant enzyme activities in hepatopancreas in pH 7.0 group changed faster than in other tissues. The results indicate that the antioxidant enzyme activities and gene expression of Chinese shrimp were induced by short-term pH stress which is the response to oxidative stress, while they were inhibited with pH stress time prolonging. It was shown that long time neutral and alkaline-induced oxidative stress probably caused the antioxidant defense system injury in Chinese shrimp. Gills and hepatopancreas could be the sensitive tissues to high and low pH stress, respectively.