Objective: In this study, we aimed to evaluate sialic acid (SA) levels and oxidative stress parameters by measuring nitric oxide metabolites (NOx), thiobarbituric acid-reactive substances (TBARS) and thiol (S) in rheumatoid arthritis (RA) patients treated with either conventional or anti-tumor necrosis factor-α (anti-TNF-α) therapy. Materials and Methods: Eighty-six RA patients and 20 healthy controls were enrolled in the study. All RA patients fulfilled the American College of Rheumatology (ACR) criteria for RA. Thirty patients were on anti-TNF-α therapy. The rest of the patients were either treated with two or three disease-modifying anti-rheumatic drugs. Health Assessment Questionnaire (HAQ) score and the Disease Activity Score 28 (DAS28) were calculated in all patients. NOx, TBARS, SA, and SH levels were measured in both patients and controls. Results: The SA levels were statistically higher in RA patients than in controls. We found increased levels of TBARS and NOx and decreased levels of SH in both groups, but these results were statistically insignificant. Spearman correlation analysis revealed positive correlation between serum TBARS levels and both NOx (r=0.322, p=0.001) and SA (r=0.242, p=0.017) levels. Conclusion: Our results confirm the role of SA in the pathogenesis of RA and its correlation with oxidative stress. Further studies on larger numbers of subjects and with longer treatment durations are needed to analyze the long-term effects of RA therapies on serum oxidative stress parameters. © Turkish Journal of Physical Medicine and Rehabilitation, Published by Galenos Publishing.