With superoxidedismutase(SOD),catalase(CAT),glutathione S-transferase(GST) and malondialdehyde (MDA) as characteristic indexes,the effects of nitrobenzene(NB) on the liver antioxidant defense system of Carassius auratus were studied under the indoors stimulant conditions,and the toxic mechanisms were discussed.The exposure concentrations of NB were 0.5,1.0,5.0 and 10.0 mg/L,and the exposure time was 5,10 and 15 days,respectively.The results show that the stress responses of four antioxidant indexes in the fish liver to nitrobenzene were different.The SOD activity was firstly inhibited and then induced.The CAT and GST activities were mainly induced.The MDA content in the high concentration group showed a significant time-effect relationship.In addition,the changes of CAT and SOD activities were not synchronous,and GST played an important part in the detoxification process of nitrobenzene. The superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST) and malondialdehyde (MDA) as characteristic indexes, the effects of nitrobenzene (NB) on the liver antioxidant defense system of Carassius auratus were studied under the indoors stimulant conditions , and the toxic mechanisms were discussed. The exposure concentrations of NB were 0.5, 1.0, 5.0 and 10.0 mg / L, and the exposure time was 5, 10 and 15 days, respectively. The results show that the stress responses of four antioxidant indexes in the fish liver to nitrobenzene were different. The SOD activity was first inhibited and then induced. The CAT and GST activities were mainly induced. The MDA content in the high concentration group showed a significant time-effect relationship. CAT and SOD activities were not synchronous, and GST played an important part in the detoxification process of nitrobenzene.