Adult mosquito collections were conducted from 1999 through 2000 at 29 US military installations located in six provinces in the Republic of Korea (ROK). Adult mosquitoes were collected in New Jersey light traps from 15 May to 15 October each year. Adult mosquito surveillance was conducted to determine the appropriate time for pesticide applications at each of the Army installations. A total of 68,051 and 62,526 adults were collected in 1999 and 2000 respectively, comprising 53,983(79.3%) females and 14,068(20.7%) males in 1999, and 50,274(80.4%) females and 12,252(19.6%) males in 2000. A total of 19 species from 7 genera were collected. The most common species collected were Anopheles sinensis(34.2%), Culex tritaeniorhynchus(29.4%), Aedes vexans nipponii(18.2%) and Culex pipiens(16.8%). Anopheles sinensis were collected at the same level while Culex tritaeniorhynchus decreased by 6.2% in 2000. The weekly population densities for some species were variable for each of the years, apparently as a result of changing weather conditions.