Introduction: The aim of this study was to determine the effect of an eight- week aerobic exercise on some immune system factors in patients with rheumatoid arthritis. Twenty – three women (age: 51.96 ± 7.73, weight: 72.37 ± 10 kg) were enrolled in the study voluntarily Methods: In this quasi – experimental random study, subjects were assigned to training and control group. The training group ( n=12)participated in aerobic exercises with the intensity of 65% reserve heart rate on stationary cycle ergometer three days a week. Both groups received the same medication during the study. Differences between groups were analyzed by independent t – test and differences inside groups were analyzed by dependent t-test. Patients' blood samples were taken before and after training period and the frequency of White blood cells, A

immunoglobulin and lymphocyte were also taken by standard methods. Results: After 8 weeks aerobic exercise, there was a significant decrease in white blood cells, BMI and also a significant increase (P<0/05).in A immunoglobulin and lymphocyte in training group. No significant differences were seen in variables between groups )P>0/05).Conclusion: It seems submaximal aerobic exercise can activate some immune system neutralization processes against damage and phagocyte factors.