The K gene is well known as a late-feathering (LF) gene which is located on the Z chromosome and induces autosexing in different feather growth-speed in the early-stage of chicks. In addition, this gene is associated with an insertion of the endogenous ev21 gene from avian leucosis virus and incomplete duplication (ID) containing a partial fusion of sperm f lagellar protein 2 (SPEF2) and prolactin receptor (PRLR) genes. In this study, we have screened two markers that capture the ev21 and ID region which were designed to identify the K gene distribution in the Yeonsan Ogye population to identify the different feathering phenotypes. For the calculation of the K gene frequency, a total of 79 birds (43 males, 36 females) were randomly investigated. If the birds have an LF phenotype, they are carrying KK or Kk+ for males and a single K genotype for females. Whereas for the early-feathering (EF), males possess the recessive homozygous alleles, k+k+, and the females have a single k+ genotype. In the male population, LF birds are 38 (88.4%) and EF birds are 5 (11.6%). Likewise, in the females, LF birds are 25 (69.4%) and EF birds are 11 (30.6%). The observed frequency of LF genotype is proper to develop LF gene-based parental line. In addition, these two markers can identify LF genotypes by identifying both ev21 and ID regions. Therefore, after phenotype validation study, these markers can be used to identify the segregation of parental LF gene as one of the effective sexing methods for the Yeonsan Ogye population.