We present a case of sphenoid sinus mucocele with recurrent visual disturbance on the same side. A 22-year-old female showed two episodes of visual disturbance in the left eye for 3 months, and acute retrobulbar optic neuritis was diagnosed. With corticosteroid, visual disturbance improved in 1 week. MRI and CT scans showed mucocele in the left sphenoid sinus, and left optic nerve swelling with high intensity was observed in T2-weighted MRI. No destruction of the optic canal was found. The contiguous inflammation in the optic nerve rather than compression was considered as pathogenesis.