B-type natriuretic peptide (BNP) and N-terminal proBNP (NT-proBNP) are both secreted primarily from the ventricle myocardium in response to the increase in volume and pressure. We aimed to investigate the relationship between the severity of mitral stenosis (MS) and the level of plasma BNP. A total of 56 patients (50 female, 6 male) were included in the study. Mitral stenosis and its related parameters were evaluated by echocardiographic methods. Patients were divided into three groups as with mild, moderate and severe MS according to their planimetric valvular area. Plasma BNP levels were measured using “Triage-B-type natriuretic peptide test” method (Biosite Diagnostics, San Diego). The relationship of BNP with mitral stenosis and other echocardiographic parameters were studied. The comparison of the 3 groups with one another revealed that the BNP level in the group with moderate MS was higher than that in the group with mild MS, however it was statistically insignificant (74.9 ± 49.7 versus 49.9 ± 40.5 pg/ml, p > 0.05). BNP level in the group with severe MS was significantly higher than that in the mild MS (144.3 ± 83.9 versus 49.9 ± 40.5 pg/ml, p < 0.001) and that in the moderate MS group (144.3 ± 83.9 versus. 74.9 ± 49.7 pg/ml, p < 0.05). When patients were taken together, as the area of the mitral valve decreased, the level of BNP underwent a corresponding increase (r:−0.48, p < 0.001). We have ascertained that the level of plasma BNP and the degree of MS are significantly correlated, and as MS becomes more serious, the plasma BNP level rises.