The present investigation was carried out in farm of the AgricultureResearchCenter belonging to Faculty of Agriculture Mansoura University to study the population density of the common mealybug species attacking grapevine trees and their associatrd predators at Mansoura district, also to evaluate the effect of certain weather factors on these insects. The obtained results showed that four mealybug species belong to order: Homoptera were recorded. These species namely, Icerya seychellarum (Westwood); Planococcus vitis (Risso); Pseudococcus longispinus(targion,tozzetti) and Maconellicoccus hirsutus Green. The results cleared that the dominant species was I. seychellarum during the two years of study as it formed 47.85% in 2009 and 39.63 % in 2010 of the total number of these insects respectively. Five predatory insects belong to three orders Coleoptera, Neuroptera and Hemiptera with a total number of 701 individuals in 2009 and 853 individuals in 2010 were recorded. Order Coleoptera was the most dominant order in the two years of study as it formed 56.78% of the total insect numbers in 2009 and 60.5% in 2010.  The results revealed that five peaks for P. vitis were found during the two years of investigation the highest average numbers for P. vitis was recorded in the second week of October in the first year and in the last week of November in the second year of study There were four peaks for P. longispinus were recorded during the two years of study. The highest average numbers for P. longispinuswas found in the last week of October in the first year while that was in the second week of October in the second year of investigation. The obtained results revealed that there were three peaks for I. seychelarum during the two years of study, the highest average numbers for I. seychellarum was recorded in last week of October in the first year, while that was in the second week of November, in the second year of study, respectively. The results showed that there were two peaks for M. hirsutus during the two years of study. The highest average numbers for M. hirsutus in the third week of September in the first year and in the end of August in the second year of study respectively. The obtained results assured that the maximum, minimum and average temperature affected greatly on the population density of P. vitis; I. seychelarum; P. longispinus and M. hirsutus during the two years of study and the maximum, minimum, average of relative humidity affected positively or negatively on the population density of these insects. The statistical correlation coefficient between the population density of Rodolia cardinalis (Mulsant); Nephus includencs Kirsh; Exocomus flavipes (Thnb.); Chrysoperla carnea (Steph.) and Orius albidipennis Reut and temperature and relative humidity showed a highly or slightly significant positively or negatively effect on population density of these insect during the two years of investigation.