Developments of the silver Y moth Autographa gamma Linn(Lepidpterra : Noctuidae) was studied at constant temperatures 20, 25 and 30⁰C⁰ ±1ْْ ⁰C . Development of immature stages was accelerated as the tested temperatures increased .Total developmental time of larval duration averaged 25.26, 19.14 and 12.08 days at 20, 25 and 30⁰Crespectively. Generation period ranged between 46.34and 23.81days depending on rearing temperature. Adult female survived slightly longer than male. Fecundity was higher at (30⁰C) than 20⁰C. Female of A. gamma deposited 106.67eggs at 30 ⁰C, while this number drastically decreased to 18.55 eggs at 20 ⁰C. However, egg hatchability was %72.41; 66.04 and 63.64 at 20,25and 30 ⁰C respectively. The threshold of development (t₀) degree- day (DDs ) was estimated to be 7.5⁰C, 10.83⁰C and 3.02⁰C for eggs, larvae and pupae, respectively. Based on estimated preferred temperature30,25 and 20 C⁰ heat units (U.T. ) 79.2, 362.5and 247.8 are required  to complied the development of egg, larval and pupal stages. Development of one generation may acquire 726.4 Degree-days.