The pathogen of hemorrhage of grass carp was studied as early as the beginning of the 1950s. Until 1978-84 the reovirus was isolated, which was denominated Grass Carp Reovirus (GCR) or Fish Reovirus. This paper deals with two hinds of virosome: one is Reovirus and the other is 24-30 nm in diameter.They were observed. in the tissue of diseased fish under electron microscope. By analysing the nucleic acid of virus, the farmer virus is dsRNA virus and the later is ssRNA virus. These two virus were infected by injection to 1 year old healthy Grass carp respectively. Two typical symptoms of hemorrhage appeared: the symptom of hemorrhage of intestinal tract caused by Reovirus and the symptom of nuasculature caused by the other virus. Tt is obvious that both viruses are the pathogen of hemorrhage of grass carp of different kinds. The v irus which is 20-30 nm in diameter was temporary defined as Picornaviridae.