Autoimmune glial fibrillary acidic protein (GFAP) astrocytopathy (GFAP-A) has been reported as a spectrum of autoimmune, inflammatory central nervous system disorders. Linear perivascular radial gadolinium enhancement patterns on brain magnetic resonance imaging (MRI) are a hallmark of these disorders. GFAP-A is associated with cerebrospinal fluid (CSF) GFAP antibody (GFAP-Ab), while the association with serum GFAP-Ab is less clear. This study aimed to observe the clinical characteristic and MRI changes of GFAP-Ab-positive optic neuritis (ON).We performed a retrospective, observational case study at the department of neurology, Beijing Tongren Hospital, from December 2020 to December 2021. The serum of 43 patients and CSF samples of 38 patients with ON were tested for GFAP-Ab by cell-based indirect immune-fluorescence test.Four patients (9.3%) were detected GFAP-Ab positive, and in three out of the four patients, GFAP-Abs were detected only in serum. All of them demonstrated unilateral optic neuritis. Three patients (1, 2, and 4) experienced severe visual loss (best corrected visual acuity ≤ 0.1). Two patients (2 and 4) had experienced more than one episode of ON at the time of sampling. MRI showed optic nerve hyperintensity on T2 FLAIR images in all GFAP-Ab positive patients, and orbital section involvement was the most common. During follow-up (mean 4.5 ± 1 months), only Patient 1 had a recurrent ON, and no patient developed new other neurological events or systemic symptoms.GFAP-Ab is rare in patients with ON and may manifest as isolated, relapsing ON. This supports the notion that the GFAP-A spectrum should comprise isolated ON.© 2023. The Author(s).