对10例重症肌无力（MG）胸腺内微小胸腺瘤进行清理形态观察。结果表明：微小胸腺瘤平均发病年龄30．9岁，约10％MG患者胸腺内有微小胸腺瘤存在，该肿瘤表现为MG的症状体征。发生部位在胸腺皮质、髓质成皮髓质交界区，因肿瘤微小，病灶多发，X线和CT检查难以发现。确诊依赖于病理组织学检查，该肿瘤的病理形态与胸腺癌相似。 The morphology of 10 cases of myasthenia gravis (MG) thymus microthymoma was observed. The results showed that the average age of onset of microthymoma 30.9 years old, about 10% of patients with MG in the thymus there is a small thymoma, the tumor showed symptoms and signs of MG. Occurrence in the thymic cortex, medulla into the skin and medullary junction area, due to small tumors, multiple lesions, X-ray and CT examination is difficult to find. The diagnosis depends on histopathological examination. The pathology of this tumor is similar to that of thymic cancer.