Abstract: The effectiveness of the antioxidant defense system in relation to the oxidative damage is of particular interest in the case of fish which show metabolic variations related to the fluctuation of water temperature1In order to clarify the relationship between temperature acclimation and antioxidant defense systemin Chinese sturgeon,Acipenser sinensis,in this study,serum reactive oxygen species (ROS) concentration,malondialdehyde (MDA) content,glutathione (GSH) content,and superoxide dismutase(SOD) activity and catalase (CAT) activity in Chinese sturgeon exposed to 12 ℃,21 ℃,26 ℃and 31 ℃were assayed1The results showed that water temperature had significant effects on serum ROS level and antioxidant defenses in Chinese sturgeon1Within survival temperature range,antioxidant defenses system in Chinese sturgeon could be a safeguard against oxidative damage resulted from ROS1The results showed that serum ROS and MDA levels increased with the increase of temperature,which ROS and MDA positively related to temperature significantly1Serum GSH level increased with the increase of temperature when temperature was below 21 ℃beyond which GSH level decreased significantly. Serum CAT activities of sturgeon stocked at different temperatures were not changed significantly during the experimental period1However,serum SOD activities of sturgeon in 26 ℃and 31 ℃ were significantly higher than those of others1The correlations between antioxidant indices and water temperature (T) could be described by nonlinear regression models,SOD =-7.7972+17.228 T-0.2821 T2 (r=0.8923, p<0.01),GSH= -146.58+ 32.3951 T-0.7427 T2 (r=0.8661,p <0.101) 1In addition,ROS content induced by elevated temperature resulted in the increase of MDA content in serum significantly1The result indicated that thermal stress caused by higher temperature (26 ℃ and 31 ℃) enhanced the production of ROS which could increase lipid peroxidation1Though elevated temperature resulted in increase of ROS contents of all treatments under lower and optimum ranges of water temperature,serum SOD activities of all treatments positively related to ROS contents1It suggested that,under the lower or optimum temperature conditions,antioxidant defenses in Chinese sturgeon maintained the homeostasis of free radicals,which made lipid peroxidation under lower level.