Abstract: Hypophthalmichthys molitrix accounts for an important proportion in Chinese aquaculture and is easily affected by the hypoxia stress. To explore the effect of hypoxia-reoxygenation stress on antioxidant enzyme activity and mRNA expression levels of Cu/Zn-SOD and Mn-SOD genes, H. molitrix with the body weight of (100±10) g was used to hypoxia experimental. Nitrogen and oxygen were inputted into the water to maintain the oxygen concentration at 2.5, 1.5, 0.5 and 0.25 mg/L for 0.5h under hypoxia stress, and at oxygen concentration of 2.5 mg/L for 3h, 6h, 12h and 24h, moreover, reoxygenation (dissolved oxygen 6.5±0.3 mg/L) for 3h, 6h, 12h and 24h in 2.5 mg/L after 24h, enzyme activity and gene expression of serum, heart and liver tissue was analyzed. The results were as follows: with the decrease of oxygen concentration the activities of total antioxidant capacity (T-AOC), catalase (CAT) and glutathione peroxidase (GSH-PX) in serum were increased, but the activity of superoxide dismutase (SOD) was firstly increased and then decreased, which was slightly lower than the normoxic level at the dissolved oxygen concentration of 0.25 mg/L. However, the SOD activity of heart and liver tissues was significantly higher than that of the normoxic level (P<0.05). The expression level of Cu/Zn-SOD and Mn-SOD of heart and liver also increased with the decrease of oxygen concentration, and the expression of Cu/Zn-SOD and Mn-SOD was significantly higher than that of the normoxic oxygen at the dissolved oxygen concentration of 2.5 mg/L (P<0.05). With the increase of hypoxia time, the activities of T-AOC, CAT and GSH-PX in serum increased significantly (P<0.05), and were significantly higher than the normoxic level after 6h hypoxia stress (P<0.05). The CAT activity in heart was lower than the normoxic level during hypoxic stress, while the SOD activity was significantly higher than the normoxic level (P<0.05), but the Cu/Zn-SOD and Mn-SOD genes were significantly lower than the normoxic level at 24h (P<0.05). The activities of T-AOC, SOD and GSH-PX of liver were significantly lower than the normoxic level under hypoxia stress for 6h (P<0.05), while the activities of SOD were significantly higher than the normoxic level under hypoxia stress for 24h (P<0.05), and the Cu/Zn-SOD and Mn-SOD genes were also significantly higher than the normoxic level at 24h (P<0.05). After reoxygenation, the activities of T-AOC, SOD, CAT and GSH-PX of serum, heart and liver could be recovered to normoxic levels, and the expression level of Cu/Zn-SOD and Mn-SOD genes in heart and liver can also be restored to normoxic levels, and the recovery time of Mn-SOD gene in liver is less than that in heart. The H. molitrix could regulate the activities of antioxidant enzymes to protect the organism from oxidative damage under hypoxia, which provide a basis references for the analysis of oxidative stress mechanism of the H. molitrix under hypoxia.