The sweet potato whitefly, Bemisia tabaci (Gennadius) biotype B was first found in southern China in 1994 and has since then become a pest of increasing importance throughout the nation. The population dynamics of this invasive species and the effect of natural enemies on its population dynamics were studied in commercial cotton fields during the summers of 2003 through 2005 in Langfang, Hebei (northern China). The abundance of Bemisia tabaci was found to increase rapidly in late July, and reached its first peak in mid-August, then followed by the second peak in early September. Whitefly populations subsequently declined slowly to attain a plateau after mid-September. A total of 13 natural enemy species were discovered in association with B. tabaci in cotton fields, including dominant species such as Chrysopa sinica Tjeder, Leis axyridis Pallas, Propylaea japonica Thunberg, Orius similis Zheng, and Eretmocerus sp. Caged experiments on velvetleaf, Abutilon theophrasti Medic, one of the preferred host plants of the insect, indicated higher B. tabaci population densities in small-mesh cages with exclusion of all natural enemies versus those in medium- and large-mesh cages, and the uncaged plants retained the lowest population densities of B. tabaci. While no natural enemies were observed in the small-mesh cages, natural enemies like Misumenopos tricuspiaata, Eretmocerus sp., Encarsia formosa Orius similis, Deraeocoris punctulatus and Scolothrips takahashii were found in medium- and/or large-mesh cages. Findings from this study suggest that under open-field conditions, various indigenous natural enemies of different sizes may act in concert in the suppression of B. tabaci populations.