Background: Oral progesterone is recommended as an alternative to gonadotropin-releasing hormone (GnRH) agonists and antagonists to prevent luteinizing hormone (LH) surge in assisted reproductive technology (ART) cycles. However, there are little data regarding its use. Objective: We aimed to compare the effect of oral Utrogestan and Cetrotide (a GnRH antagonist) on preventing LH surge in ART cycles. Materials and Methods: In this randomized clinical trial, 100 infertile women undergoing ART who received recombinant follicle-stimulating hormone (FSH) at 150- 225 IU/day were randomly assigned to receive either Utrogestan 100 mg twice a day (case group) or GnRH antagonist protocol (control group) from cycle day 3 until the trigger day. Triggering was performed with 10,000 IU hCG) when there were at least three mature follicles. Viable embryos were cryopreserved for transfer in the next cycle for both groups. The number of oocytes retrieved and transferred embryos were compared between groups. Results: The case group had significantly higher progesterone levels on triggering day, more follicles of >14 mm with higher maturity, and more oocytes retrieved with a higher rate of embryos transferred. A small increase in the pregnancy rate was observed in the case group, with no significant between-group differences. The most important result was the lack of premature LH surge in either group upon serum LH assessment on the triggering day. Conclusion: Utrogestan is an alternative treatment that could reduce the LH surge rate and increase the ART outcomes including the number of oocytes retrieved and transferred embryos compared with GnRH agonists and antagonists. Key words: In vitro fertilization, Premature luteinization, Utrogestan.