The insecticidal activity of lufenuron, chromafenozide and ecogen against the cotton leafworm Spodoptera littoralis was investigated. The results showed that the treated larvae exhibited different grades of morphological abnormalities which were positively correlated with the age of larvae and tested concentration. For all treatmetns, third instar larvae were about 4.0, 22.2 and 2.8 times more susceptible than fifth instar ones to lufenuron, chromafenozide and ecogen, respectively. Moreover, lufenuron is the most potent compound followed by chromafenozide and then ecogen.  The three compounds were efficient particularly against earlier larval stages of the insect, and their relative safety may make them useful elements if used properly on cotton and vegetable crops. The histological changes induced by lufenuron and chromafenozide in the larval body wall were also investigated. The microscopic examination revealed distinct symptoms which were closely related to the nature of the test compound.