Abstract: It was reported that aristolic acid, an active principle isolated from the root of Aristolochia indica L. , showed anti-implantation effect in mice and abortion effect in female albino rabbits, and its methyl ester also exerted abortifacient activity in mice. In order to search for new antifertility agents with simpler structure and stronger activity, eight ring opening derivatives of aristolic acid (Ⅱ_1-8) were synthesized. All the compounds and fheiv intermediates(Ⅲ_1-5) have cis-stilbene configuration and have not been reported in literature. Considering that p-coutnaric acid also exhibited anfifertility activity, five inter- mediates with such chemical feature and the eight ring opening derivatives were subjected to Pharmacological test, none of thc compounds(Ⅱ_1-8)showed antiter- tility activity in mice. It seemed that aristolic acid lost its activity by opening the phenanthrene ring. The intermediates Ⅲ1 and Ⅲ2 exerted significant action of termination of early pregnancy and anti-implantation respectively, showed the both effects in mice.