Abstract： Objective To explore the lowest effective dosage of mifepristone combined with misoprostol in terminating ultra-early pregnancy.Methods All the cases of ultra-early pregnancy classified by amenorrhea days,β-hCG and vaginal B-ultrasonic were randomly divided into two groups.One hundred cases in G1 group (minimized dosage) were orally administered 25 mg mifepristone once a day for 2 days and combined with 200 μg misoprostol 48 hours later,while 150 mg mifepristone combined with 600 μg misoprostol 48 hours later were given to 100 cases in G2 group (normal dosage).All cases were observed for 6 hours after taking misoprostol and returned for assessment three days later.Results None missing.Expulsion of conceptus:G1 and G2 group were 22 (22.0％,22/100) and 25 (25.0％,25/100;P ＞ 0.05).Failure rate:cases with incomplete abortion were 1 (1.0％,1/100) and 2 (2.0％,2/100) in G1 and G2 group,hospitalization for suspected ectopic pregnancies both was 1 (1.0％).Bleeding:bleeding cases during the administration of mifepristone in G1 and G2 group were 71 (71.0％,71/100) and 78 (78.0％,78/100; P＞0.05); the mcan bleeding time were (5.3 ± 1.4) days and (6.0± 1.5) days (P ＜0.01).Other side effects:in G1 group,majority showed light nausea (7.0％,7/100) and light abdominal pain (20.0％,20/100).Menses recovery:99 (99.0％,99/100) for G1 group and 98 (98.0％,98/100) for G2 group to recovery on scheduled time.Satisfactions:both were 99 (99.0％,99/100).Except mean bleeding days and side-effects,the differences above showed no significance (P ＞ 0.05).Conclusion It is safe and effective treatment with the lowest dosages of mifepristone and misoprostol to terminate ultra-early pregnancies.