The paper reported that the growth and reproduction of Dicrateria sp. were obviously, inhibited by monocrotophos. With the prolonging time of stress, peroxidase( POD) activity decreased, active oxygens accumulated remarkably in the cell, malondialdehyda( MDA) content and membrane permeability increased synchronously. On the contrary, the activity of superoxide dismutase (SOD) changed irregularly during the whole time of stress. The results showed that act ive oxygens resulted in cellular damage by means of lipid peroxidation, and compared w ith SOD, POD played more important role on scavenging of active oxygens.