The cotton mealybug, Phenacoccus  solenopsis Tinsley (Homoptera :Pseudococcidae) is an important insect pest worldwide causing economic damage to several crops. The insect was noticed for the first time on soybean, Glycine max L. plants (var. Giza 111) in late August using visual count during season of 2015 at Farm of Sakha Agricultural Research Station, Kafr El-Sheikh, Egypt. The mealybug was collected from the infested soybean plants during season of 2016 at Kafr El-Sheikh Governorate, Egypt and identified as P. solenopsis at Insect Identification Unit, Plant Protection Research Institute, Agricultural Research Center, Egypt. The population density of mealybug started with a few numbers at the end of August during seasons 2015, while in season 2016, the infestation began to appear nearly in mid-August, then it increased gradually till the end of the season. Generally, the population of this insect was significantly higher in the second season than the first one.  Both temperature and relative humidity had a negative and insignificant effect on the population in the two seasons with exception of effect of temperature in the second season, as it was negative and highly significant. The combined effect of the two considered weather factors was more pronounced on the population in the second season than in first one.  Generally, this study represents the first published record of P. solenopsis on soybean in Egypt.  However, the obtained results are  very important in integrated soybean management programs to avoid damage of this insect in the future.