This case report describes a traumatic aneurysm of the maxillary artery that occurred after sagittal splitting osteotomy of mandibular ramus. The patient was a 19-yearold woman. Forty days after operation, the left side of her face rapidly became swollen. An incision was made in the affected area, and the swelling resolved. Several days later, facial swelling again rapidly developed. As a vascular lesion was suspected, we perfomed angiography via the right femoral artery by the Seldinger technigue. Angiography demonstrated the presence of a traumatic aneurysm in the area of the maxillary artery. Selective embolization was performed. After following up the patient for 14 months, we have found no evidence of recurrence.