A susceptible strain and six field populations of the northern house mosquito, Culex pipiens pallens Coquillett, were collected in Seoul, Paju, Daejeon, Heongseong, Jinhae, and Buan, and tested for their susceptibility to seven insecticides by topical application. In tests with female Cx. pipiens pallens, marked regional variations of insecticide susceptibility were observed. Five field-collected populations of Cx. pipiens pallens, except for the Seoul colony, exhibited high to very high levels of resistance to cyfluthrin [resistance ratio (RR), 96-554] and deltamethrin (RR, 192-959). Low to moderate levels of resistance were observed in bendiocarb (RR, 14-46), chlorpyrifos [RR, 7-38; exceptions: Buan (RR, 63) and Jinhae (RR, 80) colonies], ${lambda}-cyhalothrin$ (RR, 5-23), S-bioallethrin (RR, 1-47), and permethrin [RR, 2-27; exception: Jinhae colony (RR, 247)]. These results indicate that careful selection and rotational use of these insecticides should result in continued satisfactory control against field populations of Cx. pipiens pallens.