The toxic effect of Abamectin and Pyriproxyfen action on the 1st instar larvae of the pink bollworm, Pectinophora gossypiella (Saund.) was studied under laboratory conditions. The toxic action of the tested compounds at their estimated LC50 values on some biological aspects of the treated insect as well as total protein content and the activity of b-esterase in the affected larvae were also studied. Based on the obtained results, abamectin was more toxic than pyriproxyfen after 24, 48 and 72 hr of treatment. In addition, the effect of treatment with the LC50 value of both tested compounds on newly hatched larvae was extended to the following developmental stages, represented as some morphological deformities. Also, total protein content in treated larvae increased than their control when Pyriproxyfen was tested but decreased when Abamectin was administered to larval diet. The electrophoretic analysis using SDS-PAGE for β-esterase enzyme in the larval stage fed on diets treated with tested compounds showed clear variation in the dense and number of enzyme bands.