Background: Rheumatoid arthritis (RA) is the most common rheumatoid disease of unknown etiology, determined by the articular cartilage destruction and bone loss. The hallmark of RA is the defect in immune tolerance. Regulatory T cells (Treg) play a critical role in the protection of peripheral tolerance. Objective: To assess the percentage of CD4+/CD25+/high/CD127low/- Treg cells in peripheral blood of RA patients as compared with the healthy individuals. Methods: The number of CD4+/CD25+/high/CD127low/- Treg cells was assessed by multicolor flow cytometry. The clinical disease activity of RA patients was determined by disease activity score 28 (DAS-28). The correlations of DAS-28 and erythrocyte sedimentation rate (ESR) with Treg cells were evaluated. Results: The percentage of CD4+/CD25+/high/CD127low/- Treg cells in peripheral blood of RA patients significantly decreased as compared with the healthy individuals (P= 0.0002). The percentage of CD4+/CD25+/high/CD127low/- Treg cells negatively correlated with DAS-28 and ESR. Conclusion: This study concludes that the defect of Treg cells plays a vital role in the pathogenesis of this disease. Further studies are necessary to determine the role of Treg cells in the clinical course of rheumatoid arthritis.