Anopheles sinensis is an important vector for Plasmodium vivax and thus has been targeted with pyrethroids in Republic of Korea. Using the direct contact mortality bioassay, two field populations of An. sinensis from Ganghwa-gun and Goyang-si were characterized for their resistance to pyrethroids with RR ratio values (Resistant ratio to imidacloprid) of 125.6 to 203.8 folds and 80.0 to 120 folds, respectively. Genomic DNA was used for Allele-specific PCR (AS-PCR) genotyping of the sodium channel genes to detect L1014S mutations. The homozygous susceptible Leu/Leu genotype in Ganghwa-gun and Goyang-si was 5.0% and 11.3% and the resistance genotypes were 95.0% and 88.7%, respectively. The homozygous Phe/Phe resistance genotype was the most prevalent as 35.4% in Ganghwa-gun and 44.0% in Goyang-si. Hence, this study suggests that malaria vector control programs should be prepared for the management of pyrethroid insecticide resistance.