Cotton bollworm, Helicoverpa armigera (Hübner) is a polyphagous agricultural pest which attacks a wide variety of agricultural crops including cotton, corn, tomatoes, sorghum, soybeans and groundnuts. Presently chemical control of H. armigera in Iran is mainly done using endosulfan, profenofos and thiodicarb. Conventional chemical insecticides such as organophosphates (OPs), carbamates and pyrethroids have caused development of resistance, resurgence and outbreaks in H. armigera populations in several countries such as Australia and Pakistan. Among the major causes of pest outbreaks are the deleterious effects of insecticides on natural enemies. In controlling H. armigera, biocontrol is important. Habrobracon hebetor Say is a valuable biocontrol agent of lepidopteran pests attacking crop plants and stored products, including H. armigera. Many broad–spectrum insecticides, especially OPs are very toxic to natural enemies. In this study, lethal effects of some conventional and biorational insecticides were assessed on H. armigera and its ectoparasitoid, H. hebetor.