Coital exanthema of Thoroughbred horses had occurred firstly in Republic of Korea. This study was performed to evaluate clinical features of coital exanthema, and provide veterinary knowledge to equine practitioner as well as horse farms. The method was clinical, clinical pathology and sexual hormone, electron microscope and libido examination. Five stallions of 27, 45 broodmares of 416 showed clinical symptoms but 124 foals and a teaser did not show any abnormal appearance. Five stallion had papule, pustule, crust around a glans, body of penis, prepuce and remain decolorized spot after treatment. One laceration of glans and 3 gait disorder had been observed but it did not affect libido. Forty-five broodmares localized had papule, pustule, crust, and ulceration around perineal region, vulva, mucocutaneous junction remain decolorized spot after treatment.