Neuromyelitis optica (NMO) and associated NMO spectrum disorders (NMOSDs) are neuroinflammatory diseases that frequently result in severe neurological disabilities. The aim of this study was to explore additional treatment options for NMO/NMOSD patients who are seropositive for anti-aquaporin 4 (AQP4) antibodies. We retrospectively evaluated the efficacy of immunosuppressants for NMO/NMOSDs by reviewing the clinical records of 52 patients confirmed as seropositive for anti-AQP4 antibodies. Of the 52 patients, 26 (23 women, three men) had received at least one kind of immunosuppressant other than corticosteroids. After eliminating ineligible cases, we evaluated the following 24 treatments in 22 patients (20 women, two men) that used azathioprine (AZA) (n = 9), cyclophosphamide (n = 1), cyclosporine A (CyA) (n = 9), tacrolimus (n = 2), methotrexate (n = 1), and mizoribine (n = 2). Both AZA and CyA treatments allowed us to decrease the median dose of the coadministered prednisone without affecting the expanded disability severity scale scores. In patients with relapsing-remitting courses, the annual relapse rate decreased from 1.7 (1.2-2.7) to 0.47 (0.36-0.59) after AZA treatments (n = 6, P = 0.028), and also showed a significant decrease from 2.7 (1.8-4.3) to 0.38 (0-0.97) after CyA treatment (n = 8, P = 0.012). These results indicate that CyA as well as AZA may help stabilize the disease activity in NMO/NMOSD patients seropositive for anti-AQP4 antibodies. This is the first case series study demonstrating the efficacy of CyA for the treatment of NMO/NMOSDs.