In the present work, polyacrylamide gel electrophoresis were used for detection the forms of esterase in the last larval instar of Pectinophora gossypiella. The larvae were treated as newly hatched larvae with sublethal concentration(LC₅₀) of three volatile oils (Petroselinum sativum, Coriandrum sativum and Cymbapoyon citratus). The larval tissues showed response towards α - naphthyl acetate and β- naphthyl acetate substrates. The esterase bands have been classified according to their reaction with three specific inhibitors (Eserine, Chlorphrifos and Fenitrothion).   The results were showed great differences in number of zones of esterase activity and in substrate specificity between treated and untreated samples. Five, four, seven and six esterase bands in untreated and (P. sativum, C. sativum and C. citrates) treated samples respectively, show activity towards α- naphthyl acetate. Six, five, seven and seven esterases were able to hydrolyze β- naphthyl acetate in previous samples arrangement. In the case of α - naphthyl acetate, volatile oils caused the increasing of arylestrases and carboxylestrases activities, while cholinesterase activity was inhibited.