Systems for artificial insemination have been established in some animals. However, due to limited availability of sperm and oocytes, more effective treatment methodologies are required. Recently, it was demonstrated that the rate of in vitro fertilization (IVF) in mice was improved by adding a water extract of licorice (Glycyrrhiza uralensis), but not glycyrrhizic acid, to the artificial insemination culture medium. In this study, we examined licorice extract for active compounds using bioassay-guided separation. The results indicated that isoliquiritigenin and formononetin were the active molecules in licorice that contributed to the improved rate of IVF. (C) 2015 The Authors. Published by Elsevier Inc.