A previously healthy 16-year-old girl developed sudden eye pain and visual loss in her right eye. On day 7 from onset her right visual acuity had decreased to light perception, and she underwent 5 courses of intravenous methylprednisolone therapy (IVMP, 1 g/day for 3 consecutive days per week). Her eye pain and her visual acuity had improved immediately. Eleven months later, follow-up MRI revealed three T2-hyperintense plaques involving subcortical white matter in the left occipital lobe, right frontal lobe, right thalamus, and thoracic spinal cord. We suspected the diagnosis as multiple sclerosis and treated with fingolimod. She developed recurrent optic neuritis (ON) on day 19 from fingolimod therapy, and we stopped fingolimod. For two years from onset she was admitted five times due to recurrences of ON and appearance of white matter lesion and myelitis. At 22 months, anti-myelin oligodendrocyte glycoprotein (MOG) antibodies revealed to be positive in her sera from the onset to the present. Our case report suggests that fingolimod might not be effective in anti-MOG antibody-related disorders together with anti-aquaporin-4 (AQP4) antibody-positive group.