The present work was carried out at Diarb-Nigm  district, Sharkia Governorate, during the two successive growing barley plants seasons 2016/2017 and 2017/2018, to study the population fluctuationsof aphids, leafhoppers and their associated natural enemies. The obtained results  showed that the aphid species were Rhopalosiphum padi (Linnaeus)., R. maidis (Fitch) and Schisaphis graminum (R.),  leafhoppers Empoasca decipiens (Paoli) and Empoasca decedens (Paoli), and predators Coccinella undecimpunctata (L.), Paederus alfierii (Koch.), Chrysoperla carnea (Stephens) and true spiders. The aforementioned insect pest were collected by two different methods from barley plants using plant sample and sweep net. The seasonal fluctuations  of the aphid species on barley plants showed  one peak at the 4^th   week of  February, the 3^rd week of February and the 1^st week March of for R. padi, R. maidis and S. graminum for the two seasons, respectively. One peak occurred at the 1^st  week and 3^rd week of February for both E. decipiens and E. decedens for the two seasons, respectively. This research aims to utilize the obtained results in developing the IPM programs against these pests on barley plants through activation the effect of both temperature and relative humidity on insect numbers.