[Objectives]  To understand the effects of photoperiod on the development and reproduction of the black cutworm, Agrotis ypsilon (Rottemberg). [Methods]  The development and reproduction of the black cutworm kept under 5 different photoperiods (0L︰24D, 8L︰16D, 12L︰12D, 16L︰8D, 24L︰0D) were observed under laboratory conditions. [Results]  The growth of the black cutworm accelerated, and the developmental duration shortened, with increasing photoperiod, whereas hatchability, survival rate, eclosion rate and average fecundity first increased then decreased. The optimum photoperiods for eggs, larvae, pupae and adults were 12L︰12D or 16L︰8D, 16L︰8D, 0L︰24D and 12L︰12D, respectively. Generally, 16L︰8D was the optimum photoperiod for the development of the black cutworm. [Conclusion]  Photoperiod had significant effects on the development and reproduction of the black cutworm, and different developmental stages had different responses to various photoperiods.