Polyacrylamide gel electrophoresis was used to determine esterase isozymes of three strains of Asian corn borer, Ostrinia furnacalis(Guenèe). Two strains were insecticide-resistant and one was susceptible. It is suggested that there were distinct differences in the zymograms of the esterase isozymes among the three strains, especially carboxylesterase. The number of cartoxylesterase bands of both resistant strains was more than that of the susceptible one, but there was no difference in thir cholinesterase. The zymograms were taken as a criterion to differentiate the resistant strain from the susceptible one. The method is suitable for studying resistance of some other agricultural insects and some aspects of methodology were discussed.