Objective: To compare the effectiveness of 600 and 800 μg of misoprostol administered intravaginally every 12 hours for termination of second trimester pregnancies.Methods: One hundred and forty-three pregnant women at 14–26 weeks' gestation were randomized in 2 groups to receive either 600 μg (N = 67), or 800 μg (N = 76) of intravaginal misoprostol every 12 hours until abortion was induced.Results: The incidences of abortion within 24 hours after initial drug administration were 82.1% (n = 55) and 78.9% (n = 60), within 48 hours 92.5% (n = 62) and 92.1% (n = 70), the mean abortion intervals were 15.2 (10.5, 20.8) hours and 15.3 (10.2, 21.8) hours, the complete abortion rates 77.6% (n = 52) and 72.4% (n = 55), and body temperature of more than 38°C were 26.9% (n = 18) and 71.1% (n = 54, p = < 0.001) in the 600 and 800 μg group, respectively. All other side-effects were similar between the 2 groups.Conclusion: In consideration of effectiveness and febrile complication, we suggest that 600 μg applied every 12 hours is the most appropriate dose to use for second trimester termination