A 39-year-old female came with the chief complaint of acute decrease of left eye vision for the past 2 weeks. No history of systemic diseases or headache was complained. The visual acuity of the left eye was "hand motion", and rapidly responded to methylprednisolone therapy in 3 days. On tapering oral prednisolone, the visual acuity decreased again from 20/20 to light perception in the left eye. The magnetic resonance image (MRI) study showed a large suprasellar mass. The patient underwent craniotomy and removal of the tumor successfully, and the pathological report turned out to be a meningioma. The visual acuity of the left eye remained poor after the surgery. In conclusion, neuroimaging study is necessary in every case of presumed retrobulbar optic neuritis which shows atypical course. Early detection of a brain tumor may save the vision of the patient.