The differentiation of sex is important for species preservation. However, Fairy Pitta is sexually monomorphic and sex of an individual is indistinguishable with its external characteristics. We determined the sex of Fairy Pitta through DNA analysis and investigated the causes and time of injury and mortality and the size based on sex. We collected 21 samples at Jeju Island, Korean Peninsula from 2004 to 2013 and extracted DNA from them and amplified chromo helicase DNA-binding gene from Z and W chromosomes through Polymerase Chain Reaction (PCR). We confirmed their sex with the banding pattern through Agarose gel electrophoresis, i.e. male (ZZ): one banded and female (ZW) two banded. We distinguished the sex of 17 of 21 samples resulting in 9 males and 8 females. Most casualties were recorded in adult of both sexes. Causes of injury and mortality proved that female casualties occurred from window strikes, dehydration, car accident, predation by natural enemies, and male occurred from window strikes, car accident and dehydration. The time of injury and mortality in adults differ by sex. There was no difference between sexes in any of the six size parameters. As the time of injury and mortality differ by sex, the survey on the role and ecological nature by sex in breeding season must be carried out in the future. External measurements may not be reliable for sexing of Fairy Pitta and other traits such as vocal or characteristics are required to identify the sex of individuals in the field.