In aquaculture, fish inevitably suffers from a variety of stressors, leading to stress response, especially oxidative stress. In fish, oxidative stress is related to the occurrence and progress of many diseases, but it is in the absence of direct evidences regarding pathogenic mechanism of oxidative stress. Therefore, the aim of this study was to investigate the antioxidative status and immune responses in common carp (Cyprinus carpio) under oxidative stress. The fish were exposed to four concentrations of H₂O₂ (0, 0.25, 0.50 and 1.00 mmol/L) for 1 h per day for 7 days. After 7 days of exposure, we collected the blood and liver tissues to determine biochemical parameters and genes expression. The data showed that the levels of cortisol and lactic acid (LA) in H₂O₂ treatments were significantly higher than those of the control group. The activities of alkaline phosphatase (AKP) and acid phosphatase (ACP) were also significantly increased in 1.00 mmol/L H₂O₂ group. In serum, 0.50 and 1.00 mmol/L H₂O₂ exposure markedly enhanced the levels of malondialdehyde (MDA) and total antioxidant capacity (T-AOC), but decreased the levels of catalase (CAT) and glutathione (GSH). In liver, 1.00 mmol/L H₂O₂ exposure obviously decreased the level of GSH, but enhanced MDA formation. Meanwhile, the genes expression data showed that 1.00 mmol/L H₂O₂ exposure up-regulated the cytochrome p450 (cyp1a) transcription and down-regulated the cyp1b transcription in the liver. Additionally, the mRNA levels of c3, c-lyz, hep and heat shock proteins (hsp70 and hsp90) in the liver were significantly up-regulated by 0.50 and 1.00 mmol/L H₂O₂ exposure. In conclusion, oxidative stress can induce stress response and lipid peroxidation, impair antioxidant ability, and initiate immune response in C. carpio. These data might contribute to understanding pathogenic mechanism of oxidative stress, and provide theoretical reference for the prevention of diseases associated with oxidative stress in fish.