The present investigation was carried out to evaluate the biochemical compound Spinosad against the cotton leafworm Spodoptera littoralis (8oisd.) using of dipping technique. The compound proved its efficacy against the 2^1°, 4^th and S^th larval instars. The obtained results showed that the 2n^d larval instars were the most sensitive to Spinosad at different tested concentrations. The 2ppm concentration could be recommended to control the r^d and 4^th larval instars of S. littorals especially in case of high population densities, while the lower concentration 0.1ppm, and even it could not prevent larval feeding but interrupt development thus prevent the appearance of a second generation. The forth and fifth larval instars were relatively more resistant to high concentrations of Spinosad. The S^th larval instars of S. littoralis could not be controlled effectively even with the highest concentration of 8ppm, as it did not prevent larval feeding. Spinosad prevent small larvae from becoming larger and more damaging. The insect dies within several days after ingesting the active ingredient with no recovery. The metamorphosis of the full grown larvae showed failure of pupation, deformed prepupae and pupae. High mortality and malformation of moths occurred. The apparently normal moths were small in size giving few numbers of small egg masses and even those tiny egg masses were sterile. The latent effect of the lowest concentration revealed to no development of the full grown larvae to normal pupae or moths, which means no extra generations of the insect.