Abstract: Effects of sub-lethal dose of Bt on parasitization, growth and development of Campoletis chlorideae Uchida were studied in laboratory. The results showed that Bt could significantly extend the vulnerable parasitizing period of Helicoverpa armigera (Hübner) larvae by C. chlorideae. With increasing of sub-lethal dose of Bt, the approximate larval pupal and adult weights of the parasitoid were decreasing. Longevity of the adult parasitoid was shortened, but developmental period of egg and larvae of the parasitoid was extending. Sub-lethal dose of Bt also had some effect on the period and weight of cocoon of the parasitoid.