Objective: To compare the respective effectiveness and safety of 600 mg and 800 mg of intravaginal misoprostol for complete abortion in case of early pregnancy failure (occurring in the first 12 weeks). Method: A total of 114 women with a diagnosis of early pregnancy failure made by transvaginal ultrasonography at Rajavithi Hospital between November 25, 2002 and July 31, 2003, were assigned randomly to 2 groups of equal size.  In one group the women received 600 mg of misoprostol and in the other 800 mg of misoprostol intravaginally.Results: The rated of complete abortion within 24 h was significantly higher in the group that received 800 mg of misoprostol (64.4%) than in the other group (45.6%) (P< 0.05). There were no significant differences between the 2 groups regarding time interval between misoprostol insertion and complete abortion or side effects.Conclusion: Intravaginal misoprostol 800 mg is significantly more effective than vaginal misoprostol 600 mg for the termination of an early pregnancy failure, with no significant differences in side effects.