Abstract: The third instar larvae of Anophles anthropophagus,An Stphensi and Aecles albopictus were treated with 0.697nmol/L and 1.393nmol/L alphamethrin,respectively.The protein content,proteinase and carboxylesterase activities in the fourth instar larvae were determined and the changes of them in three species of mosquitoes were analyzed.When compared with the control groups the protein content increased and the specific activities of proteinase and carboxylesterase decreased in the treated groups.There were significant difference between the treated and the control groups.The result also showed that alphamethrin had different infuence on different species of mosquito.