Background: Recurrent implantation failure (RIF) refers to the inability to achieve pregnancy after two or three high-quality embryo transfers, representing a significant challenge in in vitro fertilization (IVF). In these women, endometrial perfusion is diminished, and uterine artery resistance is increased. The purpose of this study was to investigate the effect of oral L-arginine on uterine artery resistance and the results of IVF in infertile women with RIF. Methods: This clinical trial was conducted on 72 infertile women, candidates for frozen embryo transfer, with a history of two previous transfer failures, who were referred to Fatemieh Infertility Center. Patients were randomly divided into two groups of control and intervention. In addition to standard drug treatment and protocol, the intervention group received oral L-arginine supplementation (3 gr daily for 20 days), beginning from the luteal phase. Uterine artery resistance index (RI) and pulsatility index (PI) were measured using two-dimensional Doppler ultrasound. Statistical analysis was performed using SPSS software, version 26, with a significance level set at less than 5%. Results: Statistical analysis revealed a significant difference in the right uterine artery RI (p<0.05), left uterine artery RI (p<0.05), clinical pregnancy rate (p<0.05), and chemical pregnancy rate (p<0.05) between the two groups. Conclusion: This study demonstrates that the daily administration of 3 grams of oral L-arginine for 20 days in women with RIF effectively reduces uterine resistance and increases both clinical and biochemical pregnancy rates.