Field experiments were conducted on cotton mealybug, Phenacoccus solenopsis Tinsley (Hemiptera: Sternorrhyncha: Coccoidea:  Pseudococcidae) which infested eggplant at Hihhya distract, Sharkia Governorate during two successive seasons 2015 and 2016. The population density, activity periods, the effects of some weather factors, number of insect generations and preferable leaf surface of of P. solenopsis were considered. The obtained results revealed that the total numbers of a live stages had four peaks of activity during the first season. They were in third week of June, third week of July, fourth week of August and second week of September. While, during the second season, three peaks of activity were noticed in the last week of June, first week of August and second week of September. The total effects of some weather factors such as maximum and minimum air temperature (˚C) and relative humidity percentage (R.H.%) showed positive significant relationship with the cotton mealybug population. P. solenopsis had three generations during the first and second seasons the first generation was taken seven weeks. While, the second and third generations took sex weeks. The first generation was during the period extended from the third week of May till the end of June, the second one took place from the first week of July till the second week of August and the third one was during the period extended from the third week of August till the third week of September. The insect pest preferred the lower leaf surface than the upper one during the first and second seasons.