Objectives: Rate of infertility in overall is around 15-10%. Intra-Uterine Insemination (IUI) is one procedure for infertility treatment. Luteal phase support defect is a main factor in fail of pregnancy. Goal of this study was to evaluate the effect of luteal phase support with progesterone suppository in patients who undergoing IUI cycles. Materials & Methods:100 infertile couples who were undergoing IUI treatment included in this study. Ovulation induction was done for all patients. When IUI was done, patients were distributed into two groups. The study group (n=50) received progesterone suppository and control group (n=50) doesn't received any medicine. Then biochemical pregnancy rate, clinical pregnancy rate and abortion rate compared between two study groups.Results: There were no differences in basic characteristics between two groups. Biochemical and clinical pregnancy were parallel in the study and control groups. There were no statistically significant increases in abortion rate between the study groups (P=0.49). Conclusion:Luteal phase support by progesterone suppository does not improve the pregnancy rate of stimulated IUI cycles.