A compound effective for the treatment of ovine theileriosis was selected and a slow-release preparation (named Kangjiaoming) was prepared. A total of 1,172 sheep and goats in Zhangjiachuan, Lintan and Yuzhong Counties, Gansu Province, where small ruminants are seriously affected by theileriosis, were injected with this preparation at a dosage of 5 mg/kg body weight. The infection rate of the control group in each of the above-mentioned counties was 98.5%, 85% and 80%, respectively. None of the treated animals became sick due to theileriosis. This drug proved to be useful for the treatment of carrier cases, although its effect was apparently slower than in acute theileriosis. The effect of the preparation on some weak animals was not satisfactory.