The present study was conducted at the experimental farm, Sakha Research station, Kafr  El –Sheikh region under field conditions during the seasons of 2016 and 2017. Results indicated that the population of the cotton leafworm moths. Spodoptera  littoralis (Boisd.) had seven peaks starting from the 3^rd week of May until the 1^st week of September during the two studied seasons. The highest number of moths was recorded during the end of June which being 8023.2 and 2063.2 moth /trap/ 30 days and 60 days after cotton planting in both seasons, respectively. The predicted peaks of generations could be detected when the accumulated thermal units recorded 525.42 DD's. The predicted peaks for the detected four generations varied from +1 to +8 days from the observed peaks. For better prediction of the cotton leafworm the period between the observed and expected peaks should be positive and as short as possible when early preparation of control materials are of great important, consequently, it could be helpful when IPM tactics are considered.