Optic neuritis is a clinical syndrome describing optic nerve inflammation, degeneration, circulatory disturbance, metabolic disorder and demyelination. The disease is characterized by acute loss of visual acuity and color vision, and ocular pain especially with the movement of the eyeball. Rarely, paranasal sinusitis may cause acute optic neuritis which is frequently treatable. Early recognition and treatment of sinus disease can avoid irreversible visual loss and improve visual acuity. We report a case of optic neuritis that seemed to be induced by paranasal sinusitis. A 6-year-old boy was presented with a 2-day history of decrease in left visual acuity. Sinus opacification was considered to be a cause of the optic neuritis. After endoscopic sinus surgery, visual acuity was improved. The detailed clinical course and review of literature is presented.