Laboratory Experiment were carried out to study the effect of different temperature's degrees, (15, 20, 25, 27 and 30 °C) on the developmental stages of the American bollworm (ABW) Helicoverpa armigera (Hübner) reared on artificial diet. As temperature increased from 15 to 30 °C the life span decreased. The lower thermal threshold for the development of ABW eggs is 13.01 °C, for larvae is 11.98 °C, for pupal stage is 9.79 °C and for pre-ovipostion period is 12.83 °C. The thermal constant for the development of eggs is 36.69 day degree (DD's), for larvae is 245.17 DD's, for the pupal stage is 181.64 DD's and 34.99 DD's for the pre-ovipostion period. The lower thermal threshold for generation of ABW is 11.54 °C and the thermal constant is 494.39 DD's. Obtained results are essential information for predicting the field population of ABW.