A preventive agent of premature ovulation which may occur during in vitrofertilization or embryo transplantation, the agent comprising a non-peptidecompound having an antagonistic effect on a gonadotropin-releasing hormone.The preventive agent shows a low toxicity, can be administered through an oralroute, and has an excellent preventive effect on the premature ovulationduring in vitro fertilization or embryo transplantation.