A four-year-old thoroughbred male horse (450 kg) who behaved in an aggressive manner toward people and other horses was referred to undergo castration surgery at the Equine Hospital, Jangsu Stud Farm and Training Center, Korea Racing Authority. Castration was performed by a closed technique using sedation (detomidine 10 mg IV) and regional anaesthesia (lidocaine) on a line 1 cm from the median raphe while the horse was standing. Incisions were made through the scrotal skin, tunica dartos, and scrotal fascia for each testis parallel to the median raphe, which was approximately 10 cm long. The testis, still capsulated by the parietal vaginal tunic, was grasped and the scrotal fascia was stripped upward from the parietal vaginal tunic using dry gauze. Then the parietal vaginal tunic, cremaster muscle, and spermatic cord were emasculated. The surgical area was disinfected without suturing. An anti-inflammatory drug (phenylbutazone) and antibiotics (benzylpenicillin + dihydrostreptomycin) were prescribed for seven days following surgery. Mild swelling and hemorrhage were observed around the region of surgery on the first day following the operation. Seven days later, no swelling or hemorrhage was observed, while formation of granulation tissue was observed in the scrotum, indicating a normal healing process.