Under the laboratory conditions, toxicological evaluation of two compoundslufenuoron & diflubenzuron against newly hatched larvae of Pectinophora gossypiella (Saund.) and biological effect of these compounds on larvae, pupae and adult emergence resulted from treated larvae were also studied. The results revealed that LC₅₀ were17.704 and 90.81ppm, for newly hatched larvae treated with lufenuoron & diflubenzuron, respectively. The obtained results show a prolongation in larval and pupal developments resulted from treated larvae by lufenuoron and diflubenzuron estimated by 21.43 and 23.16 days, respectively for larvae and 11.66 & 10.53 days for pupae. In contrast, in adult stage, the results indicated high reduction in total eggs laid, percentage of hatchability and longevity.