We report a case of eosinophilic chronic rhinosinusitis (ECRS) associated with optic neuropathy. The visual acuity in the right eye was suddenly reduced to no light perception on awakening in the morning. Fundus examination of both eyes on the same day showed no remarkable changes. Emergency computed tomography showed pan-sinusitis bilaterally and a partial defect of the sphenoid bone on the right side. From the clinical findings, the case was diagnosed as optic neuropathy associated with chronic sinusitis. Endoscopic sinus surgery (ESS) was performed on the same day, and all of the major sinuses were found to be filled with highly viscous fluid. Part of the optic canal had a defect probably due to inflammatory invasion from the adjacent sphenoid bone. Steroid therapy was started immediately postoperatively. Histopathological examination of excised polyps showed that numerous eosinophils had invaded the polyps but no hyphae were present. The patient reported that he had bronchial asthma and had had nasal polypectomy. Six months after the ESS and steroid therapy, the patient had a recurrence of the sinusitis. At that time, laboratory examination showed an elevation of total IgE and eosinophil numbers. From the clinical findings and course, this case was diagnosed as ECRS accompanied by optic neuropathy. Although ECRS rarely has ocular complications, the inflammation can spread and the optic nerve can be affected.