[Objectives] This study was conducted to investigate the toxic effect of acetochlor in loaches. [Methods]Loaches were put into the acetochlor solution with concentrations of 0,0. 062 5,0. 125,0. 25,0. 5 and 1 μl/L,respectively. The effects on dismutase( SOD),peroxidase( POD),catalase( CAT) and glutathione( GSH) activity and malondialdehyde( MDA) content in the liver of loaches were analyzed after 12,24,48 and 72 h of exposure. [Results] The activity of SOD,POD,CAT and GSH increased with the stress time and concentration,reached their maximums at 48 h after acetochlor treatment,and then decreased.However,MDA content increased with the stress time and concentration. [Conclusions] Acetochlor had obvious oxidative stress on loaches,and the activity of SOD,POD,CAT and GSH showed an obvious induction-inhibition effect with the increase of acetochlor concentration and the extension of stress time.