In the light of using of 5-imidazolinones in agriculture as safe and stable herbicides, the pesticide activities of some new synthesized derivatives 3-18 of this ring system against "cotton leaf worm (Spodoptera littoralis)" have been investigated. The interpretation of the elemental and spectral analyses proved the correct structural formulae of the new synthesized compounds. The compounds 1, 5, 6a,b, 8a,c, 9, 11, 12, 15, 16, 17, and 18 showed higher potency than chlorpyrifos (dursban) recommended insecticide. While the derivatives 2, 3, 4, 7, 8b, 10, 13, and 14 showed toxicity values less than chlorpyrifos insecticide. The 5-imidazolinones 9 and 12 may be potentially used as insecticides for treatment of cotton leaf worm.