Left atrial (LA) ball thrombus is a rare disorder. These ball thrombi are generally associated with mitral stenosis, and the restricted mitral orifice encloses the free-floating thrombus in the LA. There is a potential for fatal systemic emboli or mitral valve orifice occlusion that may result in sudden death. We report the case of a patient with tight rheumatic mitral stenosis in whom a ball thrombus was observed to bounce and rebound off the walls of LA on echocardiography. After the patient received anticoagulant therapy for 1 month, the thrombus was not found at surgery.