Objective To evaluate clinical outcomes of mild-to-moderate or moderate functional mitral regurgitation（FMR）after aortic valve replacement （AVR） in patients with severe aortic stenosis （AS），and analyze prognostic factors of these patients with mild-to-moderate or moderate FMR （2＋to 3＋）. Methods From September 2008 to December 2011，a total of 156 patients with severe AS （peak aortic gradient （PAG）≥50 mm Hg） as well as FMR （2＋to 3＋） underwent surgical treatment in Zhongshan Hospital. There were 95 male and 61 female patients with their average age of 59.2±10.5 years. Detailed perioperative clinical data were collected，and postoperative patients were followed up. The ratio of FMRpreoperative/FMR postoperative was calculated. Patient age，gender，body weight，history of hypertension，ventricular arrhythmia，atrial fibrillation （AF），left ventricular ejection fraction （LVEF），left ventricular end-diastolic diameter （LVEDD），left atrial diameter （LAD），pulmonary artery hypertension （PAH），PAG were assessed by logistic multivariate regression analysis. Results Six patients died postoperatively，including 4 patients with low cardiac output syndrome and 2 patients with refractory ventricular arrhythmia. Perioperative mortality was 3.8%. The average follow-up time was 20.3±8.5 months and follow-up rate was 85.3% （133/156）. Eight patients died during follow-up，including 3 patients with heart failure，2 patients with ventricular arrhythmia，and 3 patients with anticoagulation-related cerebrovascular accident. Multivariate regression analysis showed that FMR preoperative/FMR postoperative ratio was not correlated with age≥55 years，male gender，body weight≥80 kg，LVEDD≥55 mm，LVEF≤50%，history of hypertension or ventricular arrhythmia. However，LAD≥50 mm，PAH≥50 mm Hg，PAG≤75 mm Hg and preoperative AF were negatively correlated with postoperative FMR improvement. Conclusions Risk factors including LAD≥50 mm，PAH≥50 mm Hg，PAG≤75 mm Hg and preoperative AF are negatively correlated with postoperative improvement of FMR （2＋to 3＋）. Patients with severe AS and above risk factors should receive concomitant surgical treatment for their FMR during AVR，since preoperative FMR（2＋to 3＋）usually does not improve or even aggravate after AVR.