The present investigation was carried out to study the population density of the common mealybug species attacking mandarin trees and their predatory insects, also to evaluate the effect of certain weather factors on these insects. The obtained resultus revealed that there were four mealybug species infesting mandarin trees namely Planococcus citri Risso, Icerya seychellarum (Westwood), Icerya aegyptiaca Douglas and Icerya purchase Mask. The highest peak for P. citri in 15^th of October 2010 and 15^th of September 2012, for I. seychellarum, I. aegyptiaca and I. purchase recorded in the 15^th of September 2011 and 2012during the two successive years of study, respectively. The maximum activity of Rodolia cardinalis (Mulsant) recorded in the beginning of October 2010 (31 indiv.) and in 15^th of June 2012 (55 indiv.), Chrysoperla carnea (Steph.) recorded in 15^th of June 2011 (21 indiv.) and in 15^th of September 2012 (25 indiv.) and Nephus includens Kirsch in 15^th of September 2011 (14 indiv.) and in 15^th of June and 15^th of September 2012 (16 indiv.) during the two successive years, respectively. The highest average number for I. purchasi, I. aegyptiaca, I. seychellarum and P. citri were recorded in summer during the two years. Statistical analysis showed a highly significant differences for each insect pest between the four seasons during the two successive years of study. The highest average number of R. cardinalis recorded in summer during the two years. Also, N. includens recorded in summer during the two seasons. Meanwhile, C. carnea recorded in spring during 2010/11 and in summer during 2011/12. Statistical analysis showed a highly significant differences for each insect predator between the four seasons during the two successive years. The predator-prey ratios ranged between 40.0 in the third week of January 2011 and 9.1 in the first week of August 2011. The ratios was narrowed during the period from May to August 2011 during the second year. This ratio ranged between 29.3 in 15^th of January and 8.4 in 15^th of May 2012. The ratio was narrowed during the period from April to August 2012 during the second year. Results of statistical analysis of simple correlation coefficient indicated that, the relationship between the mealybug species and their associated predator on mandarin trees showed a highly positive significant effect for R. cardinalis, N. includens and C. carnea during the two years of study. The maximum and minimum as well as average temperature showed a highly positive significant effects on the population density of I. purchasi, I. aegyptiaca, I. seychellarum, P. citri, R. cardinalis, N. includens and C. carnea. On the other hand, the maximum, minimum and average relative humidity showed a highly negative significant effects or negatively significant effects of the population density for the previously insects during the first year. Meanwhile, I. purchasi and I. seychellarum showed insignificantly effects with minimum relative humidity during the second year.