Histopathology and ultrastructural pathology of Scylla Serrata infected by reovirus were observed by paraffin section and ultrathin section technique.The results of histopathology examination showed that the main histopathological changes found in hepatopancreas,gills,intestin canal,heart,stomach and muscle tissues.Among them,hepatopancreas,gill and intestine were the main target tissues with the most obvious pathological changes,which included damaged basal membrane of hepatopancreas,hepatocyte necrosis,clogging gill cavity,shedding epithelium of intestine,muscular fibers derangement,and fragmentation.The results of ultrastructural pathology examination showed that SsRV widely distributed in liver,pancreas,gills,heart tissue and could reproduce in these organs.Therefore,SsRV virus apparently could infect a variety of target organs.Moreover,SsRV infection caused a series of pathological changes in the target tissue cells,such as the condensation of nuclear chromatin,the increasing of electron density,the formation of myelin bodies and lysosome,the destruction of mitochondrial structure and the expansion and distortion of rough endoplasmic reticulum.