We reported successful surgical treatment of a mycotic right coronary artery aneurysm complicated by a fistula to the right atrium in a 60-year-old man admitted to hospital because of acute worsening of renal function and erythroderma. After admission, he suffered from methicillin-resistant Staphylococcus aureus septicemia. Despite administration of vancomycin hydrochloride, a low-grade fever persisted. Subacute cardiac tamponade occurred three months after admission, and acute inferior wall myocardial infarction occurred two weeks after pericardial drainage. An emergent coronary angiography demonstrated a large saccular aneurysm of the right coronary artery forming a fistula to the right atrium and obstruction of the distal right coronary artery. We emergently resected the aneurysm including the right atrial wall and repaired the defect in the right atrium. Pathological examination of the aneurysmal wall revealed its mycotic nature; the postoperative course was uneventful.