Aeromonas veronii is an acute epidemic pathogen of channel catfish (Ictalurus punctatus), causing obvious symptoms to hosts, such as distension of abdomen, enteritis and hemorrhage in multiple organs. The goal of this research was to reveal the pathogenicity of A. veronii extracellular products (ECP), and lay a foundation for vaccine and treatment. The pathogenicity of the extracellular products extracted from a high A. veronii isolated from I. punctatus was investigated in vitro and in vivo. In vitro, A. veronii extracellular products were used to detect the biologic activities and the hemolytic spectrum to a variety of erythrocyte. Then, an in vivo research on challenging the channel catfish with ECP was applied to confirm the pathogenicity. Biologic activities showed that the ECP possess lipase, protease, lecithase, DNAzyme, hemolysin; and the hemolytic effect of ECP showed a high hemolytic activity to fish erythrocyte, while no hemolytic activity in chicken and duck erythrocyte. The in vivo research on channel catfish showed that the ECP from the high A. veronii strain had an obvious pathogenicity to channel catfish, with a death rate of 100%. Diseased fish showed increasing mucus and fade spots on the skin, with eye congestion, red anus, liver hemorrhage, oedema of gill, rough surface of the spleen and intestinal expansion with thinning intestinal wall. Histopathological examination showed that edema, vacuolar degeneration, even necrosis in liver; reticuloendotheliosis spleen with few lymphocytes; and hemorrhage and necrosis of the lamella epithelia. The results of in vitro and in vivo showed that ECP of the A. veronii has a variety of extracellular enzymes, which may contribute to pathogenicity of the channel catfish.