Yeonsan Ogye is a unique chicken breed with pure black color in both skin and bones, even internal organs. It is an indigenous native chicken species in Korea which has been registered in a national treasure. Recently, Yeonsan Ogye has been suffering for the conservation problems due to differences in sex ratio. Therefore, the purpose of this study is to identify the sex ratio in unhatched eggs in the Yeonsan Ogye population using PCR amplification. The chi-square test was performed using R software to determine significant differences between the observed and expected values ​​of the sexes in unhatched eggs. The results of the experiment showed that 91 out of 153 unhatched eggs were females and 62 eggs were males. This indicated that female birds were higher in unhatched eggs than male birds (p-value < 0.05). Based on the results of this study, it is considered that the sex ratio imbalance in Ogye due to the higher mortality rate of females at the fetal stage. For the further studies, this study is very important basic research data for Yeonsan Ogye conservation and breeding programs.