The sensitivity of Aedes mosquitoes transmiting dengue hemorrhagic fever to insecticides has been evaluated in 12 sites of Ha Noi city and Quang Ninh province with the biossay procedure introduced by the World Health Organization which is currently being used in the National Dengue Control Program. The test results showed that Aedesalbopictus in Quang Ninh were susceptible to insecticides, but resistant to DDT in all of the study sites. In Ha Noi, Ae. albopictus were tolerant to most of pyrethroid (mortality, 70-96 percent), and resistant to DDT (mortality, 32-77 percent), where Ae. aegypti were still susceptible to malathion, but resistant to alphacypermethrin, deltamethrin lambdacyhalothrin, permethrin, DDT (mortality, 0-2 percent).