Abstract: In thes paper, the life tables and the interference indices of population control (IIPC) were applied as the methods to evaluate the effectiveness of several insecticides (quinphos, MIPC, buproferin) on the rice brown planthopper, Nilaparvata lugens Stal (BPH) populations after controlling the whitebacked planthopper, Sogatellafurcifera (Horvath) populations. At the same time , the population dynamics of natural enemies in paddy field were studied.1. Since the initial densities of natural enemies in paddy field were low, the population sizes of the whitebacked planthopper were controlled effectively by all these insecticides.2. The effectiveness on the BPH population, after controlling the whitebacked planthopper, were different. IIPC of the treatments spraying quinaphos or MIPC were 3. 77 or 2. 44.That is to say, the BPH population sizes would be increased by 3. 77 or 2. 44 times as that of the control. In the treatment spraying buproferin, the IIPC was only 0. 37, that the BPH population size would be decreased.3. The IIPC is an index showing the complex effect of all control factors on the pest population trend. In this case, the IIPC of the various treatments showed the effects of the insecticides on the target pest populations and their natual enemies. In the treatment spraying quinaphos, a broad spectrum insecticide, the IIPC was high. That was because the effects of the natural enemies were decreased by these insecticides. Spraying buproferin, a highly selective insecticides, affected most species of Homoptera, sparing most of the natural enemies, such as the Araneae, carabids and staphylins in the paddy field. As a result, by spraying buproferin, the control effect on the BPH population was exellent