Plasmacytoma of the spine is rather common, but solitary occurrence is not. We report two cases of solitary plasmacytomas in the thoracic spine. A 72 year old male and a 77 year old male presented with progressive paraparesis. In both cases, magnetic resonance images revealed tumors in the thoracic spine which predominantly occupied the posterior elements of the spine with compression of the spinal cord. Abnormal proteinuria and proteinemia were not detected. The tumors were removed and patients' symptoms improved, the tumors were diagnosed by histopathology to be plasmacytomas. Further neuroradiological studies suggested them to be single lesions, so that the final diagnosis was solitary plasmacytomas. Solitary plasmacytoma should be considered for diagnosis of single spinal lesion even without abnormal proteinemia or proteinuria.