The current experiments were carried out at the Research Farm belonging to the Agricultural Research Station in Sakha, Kafr El Sheikh Governorate, where onion seedlings were planted on three different agricultural dates (December, January and February) during the 2013/14 and 2014/15 study seasons to study the effect of different planting dates on the population density of the main insect pests attacking onion crop. The onion thrips Thrips tabaci Lind showed the highest number and percentage in the third planting date during the first and second season which represented by 7605 individuals (52.57%) and 7950 individuals (59.41%), respectively. The highest number and percentage of the onion aphid, Aphis gossypii Glov, the cotton leaf hopper, Empoasca Lybica de Berg and the cotton whitefly Bemisia tabaci Genn the third planting date attractive during the two successive seasons. While, the onion Maggot Delia.  Alliria Fonseca showed the highest number and percentage during the first and second planting dates during the first and second season, respectively. There were significant differences between planting dates in numbers of T. tabaci, A. gossypii, and E. lybica, whereas differences in numbers of D. alliria among planting dates were insignificant during the two study seasons.