Abstract: The predatory ability and functional response of Serangium japonicum on Bemisia tabaci (Homoptera:Aleyrodidae) were evaluated in the laboratory, and potential of the predator in controlling the pest was estimated with a semi-field cage experiment. The results showed that the adults and all-age instar larvae of S. japonicum could prey on B. tabaci of all life stages. The daily average numbers of the egg and the 1^st to the 4^th nymph of the pest consumed by a female adult S. japonicum were 640.8, 514.4, 306.0, 136.1 and 70.4, respectively. The average daily consumptions of a 1^st to a 4^th larva of S. japonicum on B. tabaci eggs were 57.8, 133.7, 403.7 and 660.9, respectively. The functional response of female adult S. japonicum on B. tabaci eggs was determined to be Holling Ⅱ type, while the attack rate (α), handling time per egg (Th) and maximum consumption per day (1/h) were calculated to be 1.0144, 0.0007 and 1366.78, respectively. Six weeks after releasing one, 3 and 5 pairs of S. japonicum per eggplant in the cage, the controlling efficacies were 55.31%, 73.25% and 84.33%, respectively, on adult pests, and, 53.82%, 83.14% and 91.79%, respectively, on immature B. tabaci (including eggs and nymphs), as compared to CK (no release of the predatory insects).