The present study was designed to investigate the possible effects of the two insect growth regulators, Diflubenzuron (Dimilin®) and Chromafenozide (Virtu®), on the ultrastructure of the cotton leaf worm, Spodoptera littoralis, ovaries. Therefore, the sublethal concentrations “LC50"(3 ppm of diflubenzuron and 0.1 ppm of chromafenozide) were applied to the 2nd and 4th larval instars. After the Dimilin®-treatment of the 2nd instar larvae (D-II), the ovary of the emerged adult moth showed the separation of outer sheath and shrunk of tunica propria as well as pyknotic follicular nuclei. By the Dimilin®-treatment of the 4th instar larvae, the emerged adults' ovary revealed irregular shaped and pyknotic follicular nuclei, degenerated microvillar region, degenerated yolk granules and signs of autolysis. Regarding the 2nd instar larvae treated with Virtu® (V-II), pyknotic follicular nuclei with irregular shape, ruptured nuclear envelope and degenerated yolk granules were observed in moth's ovary. However, Virtu®-treated 4th instar larvae (V-IV) showed follicular nuclei with irregular shape and pyknosis and the cytoplasm appeared with fragmentation of rough endoplasmic reticulum with loss of ribosomes in moth's ovary. Results showed that the effects of tested IGRs resembled the effects of insecticides on S. littoralis ovaries through distorting the cell organelles which may lead to the disruption of the ova production. These events would lead to metamorphosis failure resulting in unhealthy adults. In conclusion, results suggested that Diflubenzuron and Chromafenozide were promising, effective and safe insecticides and can be used with integrated pest management programs for controlling the Egyptian cotton leafworm S. littoralis.