Reliable non-invasive new indices reflecting severity of rheumatic valve disease would be highly beneficial. Recently, presence of fragmented QRS (fQRS) in ECG was accepted as a marker of myocardial fibrosis. fQRS is defined as the presence of RSR' patterns such as additional R wave (R'), notching in the R wave or the S wave in 2 contiguous leads. Purpose of our study was to establish frequency of fQRS in isolated rheumatic mitral stenosis compared with control group. We studied 193 patients with mitral stenosis and age/gender matched 97 healthy subjects. Patients were categorized according to the New York Heart Association (NYHA) functional class. Severity of mitral stenosis, left ventricular ejection fraction, and pulmonary artery pressure were obtained by means of echocardiography. fQRS was defined on routine 12-lead ECG. fQRS was more frequent in subjects with mitral stenosis than in control group (p < 0.001). fQRS was associated with low ejection fraction, pulmonary hypertension, poor functional NYHA class, increased mean mitral valve gradient and decreased mitral valve area (R = 0.1, p = 0.02; R = 0.1, p = 0.001; R = 0.1, p = 0.01; R = 0.1, p = 0.04; and R = −0.1, p = 0.009, respectively). Mitral valve area was the only independent predictor of fQRS in multiple logistic regression anlysis. In conclusion, fQRS is predictive of severe mitral stenosis, lower ejection fraction, inreased pulmonary artery pressure, and poor functional class. fQRS might be considered as a novel indicator of mitral stenosis severity and associated complications.