The present investigation aimed to study the effects of different photoperiods on some biological parameters of the cotton mealybug, Phenacoccus solenopsis Tinsley. This experiment was carried out in Plant Protection Department, Faculty of Agriculture, Zagazig University, Egypt during the period extended from January to November 2019. The obtained results showed that there were three nymphal instars for females. While, males have two nymphal instars and pupal stage. The suitable photoperiod for P. solenopsis females; nymphal duration, fecundity, generation and life cycle was 12 hrs. lighting followed by24 hrs. lighting which both12 hrs. lighting and 24 hrs. lighting accelerate the biological parameters than 24 hrs. darkness. On the other hand, the suitable photoperiod for males; nymphal duration, pupal stage duration, and males longevity was 24 hrs. darkness followed by 12 hrs. lighting and 24 hrs. lighting which elongated the biological parameters, with the exception of males longevity whereas the increase in lighting photoperiod decrease the males longevity. These results of this investigation should be considered effective factors for developing the integrated pest management (IPM) program.