Abstract: Acute toxicity of copper to larvae of Chironomus plumosus was studied by using the static-test method in the laboratory.The experiment was deigned to have three leves of Cu²⁺ concentration,i.e. 0.005,0.010 and 0.020 g·L^-1. Superoxide dismutase(SOD),catalase(CAT)and glutathione S-transferase(GST)activities in the homogenate of tissues of the larvae were monitored after they were exposed to the substance for 24,48,72 and 96 h,separately.Results show that Cu²⁺displayed significant effects on the activities of SOD and CAT,and such effects were significantly related to dosage of the substance.GST activity was induced after 72 h of ecposure,and peak after 96 h of exposure (P<0.01). The induction of mouthpart deformity and the developmental response with exposure to three concentrations(0.005,0.010 and 0.020 g·L^-1 )of copper for 7 days were investigated.It was found that teratogenesis of the larvae is significantly and positively related with Cu²⁺ concentration they are exposed to.