[ Objective] The study aimed to discuss the toxicity effect of abamectin and ehlorpyrifos on grass carp （ Ctenopharyngdon idllus ） and their interrela- tions. [ Method] Taking healthy and active grass carp as the object, the acute toxicity test of single pesticide and the combined toxicity test of two pesticides on grass carp were carried out. [ Result] The LC50 of abamectin and chlorpyrifes and the mixture of two pesticides against grass carp at 24, 48, 72 and 96 h were as follows： abamectin： 0.54, 0.49, 0. 17 and 0.10 rag/L; chlorpyrifes ： 0.29, 0.21, 0.12 and 0.05 rag/L; the mixture of two pesticides ： 1.22, 1.08, 0.99 and 0. 86 mg/L. The safe concentration （SC） of ahamectin, chlorpyrifos and the mixture of two pesticides were 0.010, 0.005 and 0.086 rag/L, respectively. The tox- icity of the pesticides in sequence was ablorpyrifos 〉 ahamectin 〉 the mixture of two pesticides. [ Conclusion ] Different concentrations of abamectin, chlorpyrifos and the mixture of two pesticides had remarkable effect on the growth of grass carp, the higher the concentration was, the greater the toxicity effect was. Ahamectin at low toxicity intensity had certain relief function on the toxicity of ehlorpyrifos.
