Patients with advanced heart failure often have functional mitral regurgitation. Left ventricular assist device implantation improves functional mitral regurgitation through left ventricular unloading. However, residual mitral regurgitation after left ventricular assist device implantation leads to adverse outcomes, and whether patients need concomitant mitral valve surgery is not fully elucidated. Therefore, this study aimed to elucidate the predictors of residual mitral regurgitation and to describe the temporal changes in residual mitral regurgitation. We retrospectively enrolled 15 patients with implantable continuous-flow left ventricular assist device, who had significant mitral regurgitation on echocardiography before left ventricular assist device implantation. Three patients had residual mitral regurgitation (mitral regurgitation color jet area/left atrial area >0.2) 1 month after left ventricular assist device implantation. We investigated factors associated with residual mitral regurgitation and compared patients with or without residual mitral regurgitation. On univariate analysis, mitral valve tethering area and mitral regurgitation vena contracta before left ventricular assist device implantation were significantly associated with residual mitral regurgitation (odds ratio, 1.03; p = 0.036 and odds ratio, 10.45; p = 0.0087). One month after left ventricular assist device implantation, the mean pulmonary capillary wedge pressure and pulmonary artery pressure were higher in patients with residual mitral regurgitation (pulmonary capillary wedge pressure: 11.3 ± 3.5 vs 6.4 ± 3.4 mmHg, p = 0.029 and pulmonary artery pressure: 21.3 ± 4.0 vs 15.9 ± 3.3 mmHg, p = 0.023). However, the mitral regurgitation grading and hemodynamics were not significantly different 6 months after left ventricular assist device implantation. The hospitalization-free survival was not significantly different between the two groups. Mitral valve tethering area and mitral regurgitation vena contracta were predictors of residual mitral regurgitation. Residual mitral regurgitation improved until 6 months after left ventricular assist device implantation and might not affect the prognosis.