To investigate the clinicopathological features of glycogen storage disease. Methods: The clinical and pathological data of 5 cases of late-onset glycogen storage disease were retrospectively analyzed, and the pathological morphology, special staining, and electron microscopy were observed. Results: Physical examination showed that the distal and proximal extremities and the muscles of the body atrophied evenly, muscular tension of the extremities decreased to varying degrees, strength of the cervical muscles was slightly poor, and Gewer sign was positive. Serum creatine kinase (CK) levels were increased in laboratory tests. EMG showed myogenic lesions in most cases, including 3 cases accompanied by tonic discharges and aircraft dive sounds. Under light microscopy, the fascicular membranes of muscle fibers were basically intact; there was uneven staining, the structure of myofibrils was damaged, vacuoles were formed in the sarcoplasm, and a large number of granular substances were accumulated in some muscle fibers. HE showed blue granular staining, and GMR red staining, PAS deep staining, and NADH-TR staining showed color loss. Electron microscopy showed that glycogen granules were aggregated in some myofibrils and partially dispersed, but most of them formed a membrane-enclosed cavity structure. Conclusion: Glycogen storage disease type II is a rare progressive lysosomal storage disease that exhibits autosomal recessive inheritance due to mutation of the acid alpha-glucosidase (GAA) gene on chromosome 17. Late-onset GSD type II patients usually have insidious onset. For suspected patients, diagnosis and classification can be based on the glycogen deposition in the muscles most affected by pathomorphology combined with the observation of electron microscopy and clinical manifestations. The diagnosis and classification of late-onset GSD type II patients depend on determination of the GAA enzyme or mutation analysis of hot spot genes of deficient enzymes. Recombinant human alpha glucuronidase is used in treatment of the disease, and the prognosis of patients is significantly improved.