Unruptured cerebral aneurysms can cause visual dysfunction by compressing the optic pathways. However, there are no reports of an aneurysm at the A1 segment of the anterior cerebral artery compressing the optic tract. A 69-year-old male presented with progressive right homonymous hemianopsia, and radiological examinations revealed a large, partially thrombosed left A1 aneurysm compressing the left optic tract. The patient underwent microsurgical clipping of the aneurysm, which significantly resolved the visual field defect. In cases of progressive visual dysfunction, aneurysms should be considered in the differential diagnosis. Early surgical decompression is important for optimal visual outcomes, and microsurgical clipping may be the most effective treatment.