We presented here a case of mitral stenosis developing infective endocarditis 18 months after PTMC. A 33-year-old male was admitted to our hospital for the evaluation of mitral stenosis with signs of congestive heart failure. The use of PTMC was adequately indicated based on the data of previous cardiac catheterization and was successfully performed. The post-operative clinical course was good leaving only slight mitral regurgitation demonstrated by post-valvuloplasty LVG. About 18 months after PTMC, the patient developed a high fever and erythema with tenderness on his leg, so he was admitted again. Blood culture was positive for streptococcus viridans. Moreover, echocardiogram revealed valvular vegetation on the anterior mitral leaflet, which is the characteristic finding of infective endocarditis. Antibiotics were so effective that his clinical course was relatively good with minor cerebral infarction during chemotherapy. Little is known about the prognosis and late complication of PTMC. However, our reported case may suggest that prophylactic chemotherapy might be recommended at least in some cases showing mitral regurgitation after PTMC.