Population abundance of the whitefly, Bemisia tabaci Gennadius in cotton plants was studied during 2000 and 2001 cotton seasons. The experiment was carried out at Tookh district, Kalubia Governorate, from July to early of November. The appearance of B.tabaci (Genn.) insect continued about 15-16 weeks from the beginnning of Sowing.                 Results indicated that the population density of this pest represented by four distinct peaks during the season of activity. The immature stages of B.tabaci (Genn.) occurred in high numbers on cotton leaves during the growing period and also there are 4 peaks of population were noticed. An assessment of occurrence and abundance of annual broods was approximated.                 Concerning mid to late season; the population of whitefly adults showed a fluctuation of four peaks on July, August, September and October representing by 368.75, 1000, 762 and 1977.5  individuals / 100 cotton leaves, respectively and 371.5, 1013, 873.5 and 2004 adults/100 cotton leaves, respectively during 2000 and 2001 cotton seasons, respectively.  For nymphs, four peaks were also observed on July, August, September and October representing by 336.5, 84, 93.5 and 63.75 individuals /100 cotton leaves, respectively and 404.5, 168, 80 and 72.25 nymphs /100 cotton leaves, respectively during 2000 and 2001 cotton seasons, respectively.