A modified surgical technique has been developed for repairing third-degree perineal lacerations in mares. Complications of the currently used methods include rectovaginal fistula formation, urine pooling, complete dehiscence of the repair, constipation, tenesmus and difficulty of performance in the practice. The modified method is simpler and more practical. This method was performed on eight Thoroughbred mares with third-degree perineal lacerations after delivery. The rectovestibular septum was reconstructed by three lines of sutures in a transverse direction in relation to the longitudinal axis of the rectum. In one of the eight cases pneumorectum was observed after using the new method. The conception rate obtained after using the new surgical technique was 62.5%. Pregnant mares delivered normally without any new lacerations at the subsequent parturition. It can be concluded that this new surgical technique can be used successfully for repairing third-degree perineal lacerations in mares.