Purpose This study was designed to evaluate the effects of adding Estradiol (E2) supplementation to progesterone (P) on improvement of pregnancy outcomes in poor responder patients who underwent in vitro fertilization (IVF).Methods In a prospective randomized clinical trial, 118 poor responder patients, older than 38 years without contraindications of estradiol consumption from Infertility clinic of a university hospital were randomly divided (by computerized software) into two groups. Control group (59 patients) received only P and intervention group (59 patients) received P and E2 (4 mg/d). Supplementation was done with 4 mg E2 in the luteal phase. Fertilization rate, implantation rate, biochemical and clinical pregnancy rates, abortion rate, ongoing pregnancy, multiple pregnancy and ectopic pregnancy rates were documented for those who completed the study protocol in each group (per protocol analysis) and compared between groups. Result Fifty five patients in control group and 53 patients in intervention group successfully completed the study protocol. Treatment outcomes were not significantly different between two groups. Conclusion For poor responder women who underwent IVF, addition of E2 to P supplementation could not significantly improve pregnancy outcomes.