OBJECTIVE To investigate the susceptibility to temephos, permethrin and deltamethrin of Aedes aegypti (Ae. aegypti), collected from areas with high incidence of dengue hemorrhagic fever cases in Phitsanulok Province, Thailand. METHODS The F1 progenies of Ae. aegypti colony, originated from five sub-districts including Aranyik, Hua Ro, Nai Muang, Ban Krang and Tha Pho, were used in the bioassays following the procedures of World Health Organization. For larval bioassay, the late third or early fourth-instar larvae were tested with different concentrations of temephos. For adult bioassay, the females were exposed to 0.75 % permethrin or 0.05% deltamethrin. LC50 value and mortality rate were analyzed to compare the insecticide susceptibility of the larvae and the adults in each area, respectively. RESULTS The LC50 value of temephos for the larvae from Aranyik, Hua Ro, Nai Muang, Ban Krang and Tha Pho sub-districts was 0.017, 0.017, 0.026, 0.061, and 0.113 ppm, respectively. For permethrin, the highest mortality rate (86.84%) was found in the mosquitoes from Aranyik but the others were more resistant with the lower mortality rates (16.00-42.67%). The adult mortality rates after exposing to deltamethrin were higher (82.34-98.67%) in all areas. CONCLUSIONS Ae. aegypti larvae were still susceptible to temephos. Conversely, most tested adults tended to resist the permethrin and deltamethrin.