Context: Endometrium is one of the main factors in pregnancy. During assisted reproductive technology (ART) treatments, some cycles are cancelled due to inadequate endometrial growth. Objective: This study was conducted to evaluate the effectiveness of platelet-rich plasma (PRP) in treatment of thin endometrium. Methods: a pilot study Patients: Ten patients with history of inadequate endometrial growth in frozen-thawed embryo transfer (FET) cycles were recruited into the study. Intervention: Intrauterine infusion of 0.5 ml of platelet-rich plasma that contained platelet 4-5 times more than peripheral blood sample was performed. Main Outcome Measure: Endometrial thickness was assessed. Chemical and clinical pregnancy was reported. Result: In all patients, endometrial thickness increased after PRP and embryo transfer was done in all of them. Five patients were pregnant. Conclusion: According to this study, it seems that PRP was effective in endometrial growth in patient with thin endometrium.