The calcified aortic valve has been associated with being a possible source of emboli in cardioembolic stroke. However, thrombus on the calcified aortic valve has not been identified with two-dimensional echocardiography. A seventy-two-year-old woman with calcified aortic stenosis was admitted with brain embolism. She had not previously received any platelet antiaggregant or anticoagulant. At admission, two-dimensional echocardiography demonstrated a mobile string-like abnormal echo attached to the calcified aortic valve, which showed regression and enlargement repeatedly during admission. No symptoms or clinical data suggested infective endocarditis or nonbacterial thrombotic endocarditis. After commencement of antiplatelet therapy, the abnormal echo regressed and disappeared. She continued to take the medication for seven months and then discontinued. Three months later, she developed recurrence of stroke, and an abnormal echo on the calcified aortic valve was again detected by two-dimensional echocardiography. The authors believe that the abnormal echo on the calcified aortic valve was thrombus and that it was the embolic source. Calcified aortic valve may thus be a causative lesion for mobile string-like thrombus. Two-dimensional echocardiography should be performed repeatedly in patients with calcified aortic valve and brain embolism.