It is not common for an isolated visual symptom to be the first indication of an aneurysm compressing the optic nerve. The compression can lead to blindness, and a recovery from the blindness is rare. We report a female with a left painless optic neuropathy caused by an unruptured anterior cerebral artery aneurysm. The patient had a temporal hemianopic visual field defect, which progressed to blindness in the left eye, while the right visual function was not affected. A coil embolization of the aneurysm completely restored her visual acuity to 20/20. These findings suggest that aneurysmal lesions should be ruled out in case of unilateral optic neuropathy with hemianopic visual field defects and progressive visual loss.