 Azathioprine is an immune-modulatory agent which is available in the oral form and dont require hospitalization to be administered, however, because of side effects such as bone marrow suppression and hepatotoxicity, periodic check of blood cells and liver enzymes are needed. Rituximab is a cluster of differentiation antigen 20 inhibitor which leads to decreased B lymphocytes and antibody in patients. This medication is only available in the injectable form and needs hospitalization to be administered. Close monitory is needed during the administration considering severe side effects such as allergic reactions and respiratory distress. However, laboratory tests are not needed in patients taking rituximab although it is more expensive than azathioprine. No clinical trial has been performed previously to compare clinical efficacy of these two drugs in NMO-SD patients. Therefore, we aimed to compare their efficacy through a randomized clinical trial. 