PURPOSE: We purposed to determine the outcomes of surgical mitral valve repair in patients with atrial septal defect (ASD) and mitral regurgitation (MR) and determine factors associated with good outcomes. METHODS: Sixty-one patients after operation for ASD and MR were enrolled. Mitral valve annular diameter, lengths of mitral leaflets, and motion angles of both leaflets were measured on echocardiographic images. RESULTS: The severity of MR and mitral valve prolapse improved after surgery from 2.3±0.7 to 1.7±0.9 and from 41.8% to 16.4%, respectively. In patients with postoperative MR grade <3, angles of both leaflets on systole and motion angles of the posterior leaflet were changed. Operation at an earlier age (28.0±18.9 years vs. 60.3±10.1 years) and chordae repair (70.2% vs. 25.0%) were performed more frequently in patients with postoperative MR grade <3. More MAZE operations were performed in patients with postoperative MR grade ≥3 (21.3% vs. 87.5%). CONCLUSION: Operation age, MAZE operation, and chordae repair affected postoperative MR. Not only prolapse, but also the angles of both leaflets on systole and the motion angle of PML were significantly improved in patients with postoperative MR grade <3.