Neuromyelitis Optica Spectrum Disorders (NMOSD) is associated with a pathological humoral immune response against the aquaporin-4(AQP-4) water channel. Belimumab (Benlysta ®) is a human immunoglobulin G1λ monoclonal antibody that inhibits B-cell survival and differentiation by neutralizing soluble B lymphocyte stimulator. Belimumab may benefit some patients with NMOSD due to the important role of B cells in the pathogenesis of NMOSD. Clinical trials may be needed to observe its efficacy and safety.

The investigators primarily aim to observe the number of attacks from initiation of belimumab treatment.

The secondary outcomes are to determine: The safety profile of belimumab in participants with NMO and whether belimumab improves Expanded Disability Status Scale (EDSS), et al.

Inclusion Criteria:

1. Male or female patients ≥ 18 years old
2. Diagnosis of NMO or NMO spectrum disorder according to the 2015 International Panel for Neuromyelitis Optica Diagnosis criteria
3. Clinical evidence of either at least one attack requiring rescue therapy (intravenous corticosteroids, intravenous immunoglobulin, plasma exchange, or a combination of these therapies) in the year before screening or at least two attacks requiring rescue therapy in the 2 years before screening.
4. EDSS <= 6.0
5. Patients were seropositive for AQP4-IgG
6. Able and willing to give written informed consent and comply with the requirements of the study protocol.

Exclusion Criteria:

1. Current evidence or known history of clinically significant infection (Herpes simplex virus, varicella-zoster virus, cytomegalovirus, Epstein-Barr virus, human immunodeficiency virus, Hepatitis viruses, Syphilis, etc)
2. Participation in another interventional trial within the last 3 months
3. Tumor disease currently or within last 5 years
4. Pregnant, breastfeeding, or child-bearing potential during the course of the study
5. Clinically relevant heart, liver, kidney or bone marrow function disorder