Aim: The aim of our study is to determine the efficacy and value of two doses of vaginal progesterone suppository on the outcome of threatened abortion. Material and Method: 220 pregnant women who presented in first trimester of pregnancy (6-12 weeks) with mild to moderate vaginal bleeding and positive embryo cardiac activity by ultrasound, randomly divided by (computer generated random table) into two groups each group contain 110 women, group (I) received 400mg vaginal progesterone suppository (intervention group) &group (II) received 200mg vaginal progesterone suppository (control group). The treatment considered successful if pregnancy continued beyond 18 weeks of gestation. Results : There was statistically significant difference between group I & group II as regarding pain in the (2nd 3rd, 4th week) with (p value 0.026, 0.050, 0.036) and there was statistically significant difference between group I & group II as regarding bleeding in the (2nd, 3rd, 4th week) with (p value 0.043, 0.010, 0.004). Pain and bleeding was less with group I (progesterone 400 mg) in the 2nd, 3rd, 4th week (follow up of the patients). In 220 of threatened abortion, there were 60 cases of abortion, the incidence of abortion in the group I was 17.9% (20/110) and in the group II it was 37.0% (40/110) and the difference was statistically significant (p value 0.001).The success rate in continuing pregnancy beyond 18 weeks gestation in the group I was statistically significant higher than that in group II (82.1% vs. 63.0%; p<0.05). After 13 weeks gestation, 6(6.5%) in group I had cervical cerclage and 12(17.6%) in group II had cervical cerclage. At a follow-up three dimensional ultrsound performed after 22 weeks of gestation, 8 women in group I & 12 women in group II were found to have low lying placenta, 2 women in group I & 2 women in group II were found to have placenta previa, 2 women in group II were found to have hydrops fetalis, 2 women in group I were found to have placenta accreta. Conclusions: Treatment with 400mg vaginal progesterone suppository appears to have beneficial effects on the outcome of threatened abortion. However, treatment of threatened abortion with progesterone is still controversial, and large-scale, multi-center, randomized controlled studies are still needed to confirm the efficacy of progesterone in the management of threatened abortion.