The authors report a rare case of fungal endocarditis caused by Histoplasma capsulatum in an immunocompetent woman with mitral valve prosthesis. The patient presented with chronic fever and embolic phenomenon. Transthoracic and transesophageal echocardiography revealed a mobile mass attached to mitral prosthetic valve and her blood cultures were negative for both bacteria and fungi. The diagnosis was made by presence of budding yeasts in the histopathological findings of the vegetation and recovery of H. capsulatum from tissue culture of the excised vegetation. The patient was improved after a 6-week course of amphotericin B. Fungal endocarditis caused by Histoplama capsulatum is rare but should be considered as a possible causative organism in culture-negative endocarditis. To our knowledge, this is the first case report of H. capsulatum endocarditis in Thailand.