Abstract Backgrounds Percutaneous balloon mitral valvuloplasty (PBMV) is the treatment of choice for anatomically suitable severe rheumatic mitral stenosis (MS). Atrial fibrillation (AF) is one of the most common arrhythmic conditions in rheumatic MS and may decrease successful or alter the long-term outcomes of rheumatic MS patients who are undergoing PBMV. Purpose The purpose of this study is to investigate the long-term outcomes of treatment in patients with AF compared to sinus rhythm (SR). Results Post-PBMV median follow-up time was 10.83±5.69 years. The incidence of the primary endpoint was 57.8% (95% confidence interval [CI]: 48.6% to 66.9%) and 20.0% (95% CI: 10.3% to 29.6%), p-valve <0.001 in AF and SR patients respectively. The adjusted hazard ratio (HR) of the primary endpoint in the AF compare with SR group was 2.377 (95% CI: 1.250 to 4.520, p-valve = 0.008). Not only the rate of death that was greater in AF than SR group with 30% (95% CI: 22% to 39%) and 11% (95% CI: 4% to 19%), p-valve <0.001 respectively but also as in MV surgery, the incidence rate was 30% (95% CI: 22% to 39%) and 10% (95% CI: 2% to 18%). Independence predictors of the primary endpoint were age >55 years (hazard ratio [HR]: 1.765; 95% CI: 1.05 to 2.95, p=0.031) and echocardiographic score >8 (HR: 2.94; 95% CI: 1.22 to 7.09, p=0.017). The MiTrAL-55 score has a C-statistic of 0.71±0.036 reflecting the good ability to predict long-term outcomes. Conclusion Severe rheumatic MS patients with AF had a worse long-term prognosis than SR after PBMV. An early decision to PBMV in patients with MS supporting with the predictive scoring system to minimize morbidity and mortality is necessary. Funding Acknowledgement Type of funding sources: None.