Four-channel aortic dissection is quite rare, and is a highly life-threatening situation predisposing to aortic rupture. We report the case of a 70-year-old woman with non-Marfan syndrome. She was evaluated at our hospital for the diagnosis of another disease. She had no symptoms. Enhanced CT revealed an ascending aortic aneurysm, 68 mm in diameter with four-channel dissection. Because of the high risk of rupture, we performed ascending aortic replacement under deep hypothermia. The cardio-pulmonary bypass (CPB) was not discontinued due to right ventricle failure. Coronary arterial bypass grafting (CABG) to the right coronary artery using the great saphenous vein was added. Even after additional CABG, CPB was not discontinued. The surgery finished under percutaneous cardiopulmonary support (PCPS). PCPS was removed on the third postoperative day. Her postoperative course was uneventful, and she was discharged without any abnormal condition. Four-channel aortic dissection has a high risk of rupture, suggesting the need for early surgical treatment.