The larvicidal activities and repellency of Magnolia kobus extract against C. pipiens and Ae. albopictus were examined. M. Kobus methanol extraction showed 100% larvicidal activity both two mosquitoes at 500 ppm after treated 24 h. At a concentration of 50 ppm, the hexane fraction showed 100% and 94% mortality against C. pipiens and Ae. albopictus at 24 h, respectively. Purification of the biologically active constituents from the hexane extraction with larvicidal activity was done using silica gel open column chromatography and HPLC. H2 fraction gave >90% mortality to both mosquitoes at 10 ppm after treated 48 h. H21 fraction was determined 100% larvicidal activity to C. pipiens at 10 ppm. However, very low larvicidal activity was obseved to Ae. albopictus. This is considered a synergistic effect between substances. It also appears that there is a susceptibility difference of substance against mosquito species. H21 fraction was analyzed as the lignan, sesamin (C20H18O6) by GC-MS and NMR. Mosquito repellent and olfactory response was using a patch test.