Women usually request an abortion when they have experienced an emergency contraception (EC) failure; this population represents 13% of all early pregnancy terminations in China. Many women would prefer to choose a medical abortion in order to avoid anesthesia, over a surgical operation. However, medical termination of a pregnancy after mifepristone EC failure has not been studied although it has already been extensively practiced by empirical means in China. There is no clarification in literature as to whether mifepristone is still effective in medical abortion with its previous failure experience in EC. This randomized study was aimed to compare the efficacy, safety and acceptability of pre-treatment with mifepristone and misoprostol compared to misoprostol alone in the medical termination of pregnancy by mifepristone EC failure.