Multiple sclerosis (MS) is an immune-mediated disease characterized primarily by inflammatory demyelinating lesions in the central nervous system (CNS), with the white matter being predominantly affected. Its etiology remains unclear and may be associated with various factors such as genetics, environment, and viral infections . Pathologically, MS presents as multiple demyelinating lesions in the CNS, which may be accompanied by damage to nerve cells and their axons. Lesions on MRI show characteristic distributions, morphologies, and signal intensities . MS typically onset in young adults and is more common in women. Frequent symptoms include visual decline, diplopia, limb sensory disturbances, limb motor impairment, ataxia, and bladder or rectal dysfunction . As MS can lead to varying degrees of neurological deficits, and repeated relapses result in disability progression, it impacts patients' normal lives and work, posing a significant burden on individuals, families, and society. Considerable progress has been made in MS treatment in recent years, with agents such as teriflunomide, fingolimod, siponimod, and dimethyl fumarate having been approved for marketing in China. In the two concurrently conducted active-comparator trials, ASCLEPIOS I and II, involving patients with relapsing multiple sclerosis, the annualized relapse rate was significantly lower in the ofatumumab group compared to the teriflunomide group. Ofatumumab was also superior to teriflunomide in suppressing MRI lesion activity . Although the aforementioned studies have confirmed the clinical efficacy of ofatumumab in treating MS, data from Chinese populations are lacking. Its clinical effectiveness, safety, and optimal treatment timing require further support from real-world evidence. Exploring more indicators to predict MS disease activity and progression is crucial for identifying high-risk patients, assessing prognosis, and evaluating treatment response. Neurofilament light chain (NfL) is a specific biomarker for neuroaxonal damage, released into the cerebrospinal fluid (CSF) and serum after axonal injury . Serum and CSF NfL concentrations are highly correlated. Numerous studies in recent years have shown that high sNfL levels are associated with active T2 lesions and relapses, as well as brain volume loss. sNfL can not only monitor disease activity and treatment response at the group level in MS patients but also predict disease course, making it a valuable biomarker for predicting MS relapses and disability progression. It helps identify patients at higher risk of future disease activity and assists in clinical decision-making. Previous data from ASCLEPIOS I and II demonstrated that ofatumumab significantly reduced sNfL concentrations at the first assessment (Month 3) and at all subsequent visits in patients with RMS . However, existing studies have not included data from Chinese populations. This study aims to address this data gap for this specific population.