Objectives: To assess resistin expression in serum and synovial fluid from patients with rheumatoid arthritis and osteoarthritis and to study its relationship with rheumatoid arthritis disease activity.Patients and methods: This study included fifty patients, 25 rheumatoid arthritis patients in addition to 25 osteoarthritis patients served as control group. Serum and synovial fluid resistin were measured. All patients were subjected to full history taking, full detailed clinical examination, laboratory assessment, Assessment of disease activity according to DAS 28 score, Serum and synovial fluid samples from effused knees were obtained from all patients and controls and tested for resistin level. BMI was calculated for patients and controls. Results: Serum resistin level in RA patients was higher than those with osteoarthritis (p>0.01), also synovial fluid resistin level in RA patients were higher than those with osteoarthritis (p>0.001), however there was no correlation between resistin level and disease activity score (DAS 28) (p=0.274) or inflammatory markers as CRP (p=0.193) and ESR (p=0.265).Conclusion: Resistin level was found to be higher in serum and synovial fluid of RA patients compared to OA, this in addition to the up-regulated resistin at local sites of inflammation suggest a role for resistin in the pathogenesis of rheumatoid arthritis. The non-significant statistical correlation between resistin and DAS28 in our study suggest that many factors may affect resistin level in RA and not only the disease activity. Further studies including a large number of patients should be directed towards the relationship between resistin and RA disease activity.