The present investigation aimed to study the effect of three constant temperatures (20, 25, and 30°C) on the development of the black cutworm, Agrotis ipsilon (Hüfnagel). The incubation period, larval duration, pupal duration, pre-oviposition period and duration of generation were estimated. The time required for development was decreased as the temperature increased from 20 to30 °C. The lower threshold temperatures (t₀) was 11.49°C for eggs, 10.63 °C for larvae, 9.83 °C for pupae, 11.06 °C for pre-oviposition period and 10.53 °C for generation. The average thermal requirements needed for completing the development were 51.3, 303.5, 183.5, 38.1 and 575.3 degree-days for eggs, larvae, pupae, pre-oviposition period and generation, respectively.