The effectiveness of Eretmocerus sp. and Aschersonia aleyrodis in controlling Bemisia tabaci populations on cucumber were determined in separated and combined greenhouse experiments. The results showed that after spraying A. aleyrodis (5 x 10(6) spores per ml, twice per generation) and releasing Eretmocerus sp. (3 female per plant, twice per generation), 95.74% and 57.58% of whitefly populations were controlled, respectively. However, when the two natural enemies were used together with the same rate mentioned above (A. aleyrodis spraying twice followed by releasing Eretmocerus sp. once or twice in one generation), 97.02%-97.91% of whitefly populations were controlled. Moreover, the increasing index of whitefly population (I) subjected to both natural enemies together was below I, indicating the substantial reduction in whitefly population. The combined treatments provided a better control effect of whitefly than separated ones, and there was no contradicted effect between both natural enemies.