Abstract: The molecular stryctures and absolute configurations of α-and β-anordrins are reported.Animal experiments showed that pure α-epimer possessed high anti-implantation and anti-early pregnancy effects,but the pure β-epimer exhibited very low effects at the same dose.MNDO program was applied for the optimization of the configurations of epimers to establish the isolated molecular configurations and calculate the quantum chemical indexes.The results showed that the configurations and the differences of action field in three-dimensions of α-and β-epimer are probably the factors that the α-epimer exhibited biological activity.