Left atrial thrombus, which is a frequent finding in patients with mitral valve disease, is generally attached to the atrial wall. Left atrial free-floating thrombus has rarely been reported. Since the risk of peripheral emboli is fairly high, patients with such a thrombus are candidates for emergency surgery. Our first case was a 45-year-old female with mitral stenosis and regurgitation. The typically appearing free floating thrombus with a diameter of 3.4 cm was detected by two-dimensional and M-mode echocardiography, and an appropriate surgical procedure was performed. The surgical findings were consistent with the echocardiographic findings. Our second case was a 59-year-old female. A free floating thrombus with a diameter of 2 cm was detected by echocardiography when this patient with mitral stenosis was hospitalized because of right hemiplegia and aphasia. The thrombus was extracted by an immediate surgical procedure. Transthoracic echocardiographic (TTE) study was definitely specific in both cases; no other study was thus required.