The objective of this study was to compare the persistence of 3 different insecticides used to impregnate mosquito nets. These were Deltamethrin 25% tablet at an average concentration of 25-30 mg/m2, Bifentrin 25% (25-30 mg/m2) and Cyfluthrin 5% EW (40-50 mg/m2). The study was carried out in the field areas under the responsibility of the Office of Disease Prevention and Control No. 11, NakornSiThammarat province (ODPC 11). Anopheles minimus mosquito, aged 3-5 days, full feeding with blood or 10% sugar, obtained from the insectariums of the ODPC 11 and Bureau of the Vector-borne Diseases were used to conduct bioassay test 6 months after the impregnation. The results showed that after 6 months, the unused and never been washing mosquito nets impregnated by 3 different insecticides (Deltamethrin 25% tablet at an average concentration of 25-30 mg/m2, Bifentrin 25% [25-30 mg/m2] and Cyfluthrin 5% EW [40-50 mg/m2]) were still able to kill the tested mosquitoes 85, 87.5 and 80%, respectively. It was implied that these insecticide treated mosquito nets were effective for controlling malaria vectors for at least 6 months.