Objective To evaluate midterm and longterm clinical outcome of bilateral internal mammary artery composited Y grafts for coronary artery bypass grafting (CABG)， analyze risk factors for late death ，and to improve surgical results. Methods Between January 2000 and May 2004, One hundred and sixtyfive patients underwent bilateral internal mammary artery grafts for CABG, The clinical data, postoperative complications and survival results were retrospectively reviewed and analyzed. The preoperative and postoperative cardiac function was compared. All factors that may have affected the survival were analyzed by logistic regression, to identify significant variables associated with late death. Results Total 561 anastomosis sites of internal mammary arteries were completed with each patient received an average of 3.4 grafts. There were no perioperative deaths. There were 16 patients with postoperative complications including recurrent angina, myocardial infarction, low cardiac output syndrome, sternal infection and so on. All patients were treated conservatively without reoperation. One hundred sixty patients（97%）were followed up of 5.6±1.2 years, there were 23 late deaths including 10 patients of cardiac related death in which 3 had recurrent myocardial infarction, 4 heart failure, and 3 arrhythmia; 13 patients of nocardiac related death in which 4 upper gastrointestinal hemorrhage, 3 cancer and 6 uncertain cause. 25 patients had major cardiac related events including recurrent angina 18, myocardial infarction 4, repeated revascularization 3. Left ventricular ejection fraction [CM(159mm]was significantly improved as compared with that before operation（54%±6% vs. 43%±12%, Plt;0.05）. The 1-, 3-, 5-year actuarial survival rates and eventfree rates were 98.2%±0.3%, 96.2%±0.5%, 90.5%±1.9% and 95.5%±1.2%, 91.3%±2.1%, 86.6%±1.5%, respectively. According to statistical analysis, univariate analyses had proved that advancing age＞65 years，diabetes，ejection fraction(EF) less than 30%，the New York Heart Association (NYHA) class Ⅲ/Ⅳ, and low cardiac output syndrome required placement of the intraaortic balloon pump were predictors associated with hospital major adverse cardiac events (Plt;0.05). Those variables entered into the logistic regression model and found to be independent predictors associated with increased late cardiac death included advancing age ＞65 years(OR=11.6), diabetes (OR=21.4), EF less than 30%(OR=37.5) and NYHA class Ⅲ/Ⅳ(OR=40.2). Conclusion Patients receiving bilateral internal mammary artery composited Y grafts have better longterm survival and reduced cardiac related events. Independent risk factors for late death are NYHA function class Ⅲ/Ⅳ, EF less than 30%, diabetes and advancing age ＞65 years.