Objective: Several studies have shown the improving effect of heparin on the outcomes of ART. Moreover, it has been reported that adding heparin in non-thrombophilia patients with RIF is useful. The aim of this study was to evaluate the beneficial effects of heparin on ART outcomes in women with history of recurrent implantation failure (RIF) and without history of congenital or acquired thrombophilia in a randomized, controlled clinical trial (RCT).Materials and methods: In this study, 100 patients with a history of two or more failures in implantation in cycles of ART were randomly subdivided into two groups of study and control. Patients of the control group just received the luteal phase support. In the patients of study group, in addition to the routine support of luteal phase following in vitro fertilization (IVF) or intra cytoplasmic sperm injection (ICSI), 5000 units of subcutaneous heparin was administered for 15 days from the day of oocyte pick up. Pregnancy test (b-HCG) was done for patient of two groups 15 days after IVF.Results: In the study group, pregnancy test was positive in 16 (32%) patients and negative in 34 (68%) patients. In the control group, pregnancy test was positive in 15 (30%) patients and negative in 35 (70%) patients. There was no significant difference between two groups for the role of heparin in the pregnancy rate (p=0.5).Conclusion: Although the effect of heparin on pregnancy was not statistically significant in this study, with regard to the numerous benefits of this agent, it is recommended to study its effects in further studies with lager sample size.