This study was conducted to determine the comparative toxicities of pyriproxyfen and thiamethoxam on the sweetpotato whitefly, Bemisia tabaci biotype B. Ovicidal effect of pyriproxyfen (100 ppm) showed 94.5%, which was 8 higher times than that of thiamethoxam (50 ppm) at the recommended concentration, The nymphal mortalities of both insecticides treated on the 3rd instar stage were over 85%. Thiamethoxam was very effective against adults, but the activity of pyriproxyfen was relatively low. Longevity and fecundity of newly emerged adults from the treated pupae of two chemicals were adveresely affected. Unlike pyriprezyfen, thiamethoxam highly showed root up-take systemic effect on nymphs and adults of B. tabaci. Pyriproxyten and thiamethoxam showed residual effects against B. tabaci and particularly, thiamethoxam maintained high control effect with over 90% up to 7 days after treatment. In the control efficacy test on B. tabaci, the control values of pyriproxyfen and thiamethoxam at 9 days after treatment were 92.0 and 99.3%, respectively.