Background: We aimed to investigate the characteristics and echocardiographic changes in patients with severe mitral stenosis (MS) who maintained sinus rhythm (SR) for at least 10 years after successful percutaneous mitral balloon valvuloplasty (PMV). Methods: We retrospectively reviewed 107 patients who had successful PMV and follow-up echocardiography for at least 10 years without mitral valve surgery. Preprocedural, immediate postprocedural (PMV), and long-term follow-up echocardiography (at least 10 years after PMV) data were reviewed. Results: The mean follow-up time after PMV was 15 ± 4 years for SR patients (n = 50) and 16 ± 4 years (p = 0.172) for atrial fibrillation (AF) patients (n = 57). The left atrial diameter was significantly decreased in SR patients in the follow-up echocardiography images compared to its pre-PMV value (46.7 ± 6.3 vs. 43.3 ± 6.2 mm, respectively), whereas it was significantly increased in patients with AF (53.9 ± 7.1 vs. 58.1 ± 8.7 mm). In multivariate analysis, preprocedural AF (odds ratio [OR] 14.50, p = 0.001) and LA diameter ≥50 mm (OR 8.81, p < 0.001) were independently associated with increased risk for the presence of AF after successful PMV. Conclusion: Very long-term maintenance of SR after successful PMV was associated with preprocedural SR and LA diameter < 50 mm.