This survey is performed for the vector mosquitoes including of Japanese encephalitis, Malaria and West niles virus. Black light traps were installed in 5 sites (Sejong lake, Janggun-myeon, Jeonui-myeon, Yeongi-myeon, Bukang-myeon). Mosquitoes were collected twice every week from five collection sites using a black light trap from May to September. A total of 10 species belonging to 4 genera, 14,234 female mosquitoes were collected and identified as vector mosquitoes. Among ten mosquito species, Culex pipiens complex was the most commonly mosquitoes (6,163 individuals, 43.3%). The greatest number of Culex pipiens pallens was trapped in the first week of July. A total of 115 pools from 14,234 mosquitoes were prepared according to their species, collection date and site. We have screened infection of virus in mosquitoes. All of virus were not detected in mosquitoes. Our findings confirm that population and first appearance time of vectors mosquitoes and virus infection in Sejong city.