Abstract: The clinical and ultrastructural changes were studied in 5 Gases suffering from muscle phosphorylase deficiency（McArdle’s disease or glycogen storage disease,type V） which is a type of hereditary myopathy.The clinical features included muscular cramps after muscular exertion（in all cases）and episodes of myoglobulinuria（one case）,the electron-microscopical findings of the muscle biopsy showed monogranular particles of glycogen freely dispersed in the cytoplasm of myofibrils or filaments of the“I”bundles, with a tendency to produce large aggregates beneath the sarcolemma.The changes of mitochondria included an increase in number,swelling and pyknosis,the sarcolemma exhibited comb-like denticular protrusions,their longitudinal axes being parallel to Z-bundles of myofibrils,the basement membrane was locally thickened on the top as well as at the bottom of comb-like denticular protrutions.These findings might indicate the result of atrophy of myofibrils and increase in interstitial tissue.