Current research has focused on the inhibitory effects on the reproductive organs of cotton leafworm, Spodoptera littoralis resulting from 4^th instar larvae treated with sublethal concentration (LC₂₅) of methoxyfenozide. Results showed elongation in the immature stages and longevity of adults than control, as well as reduce pupal weight, oviposition period, fecundity and hatchability percentages. Anatomical structures of virgin moths surviving from larvae treated with LC₂₅of methoxyfenozide showed general atrophy and abnormal features for ovaries and testes than thatof untreatedones. Histological disruptions were recorded in ovaries in vitellogenesis and post vitellogensis stages as deformation in follicular shape, clumping of the chromatin material in nurse cells and disorganization of yolk and appearance of vacuoles between yolk and chorion. While in treated testes the testicular wall disappeared and vacuoles between follicles take place. Methoxyfenozide caused alterations in the amounts of both total soluble protein and total lipids and also in the activities of acid and alkaline phosphatases and phenol oxidase in the ovaries and testes of the resulted adults as compared to control adults.