The purpose of the clinical study was to compare the efficacy and side effects of 10 mg of mifepristone alone (Group 1) and with 20 mg of tamoxifen (Group 2) for emergency contraception, especially as used within 72-120 h after coitus. Four-hundred female volunteers with one act of unprotected intercourse or contraception failure (200 cases in each group) were recruited and completed the study. There were 198 women treated < 72 h after coitus (100 in Group 1 and 98 in Group 2), whereas the remaining 202 patients were treated between 72-120 h (100 in Group 1 and 102 in Group 2). In total, four pregnancies occurred; one treated < 72 h in each group, two between 72-120 h in Group 1. Efficacy for prevention of unwanted pregnancy by Trussell method is 84% for Group 1, and 95% for Group 2, and which is not significantly different between the two groups and even subgroups. The side effects (15.5% for Group 1 and 14.5% for Group 2) and changes in menstruation were infrequent and mild in both groups. Further studies should be conducted to determine whether tamoxifen combined with mifepristone for emergency contraception is more effective as compared with mifepristone alone.