The study focused on bacteriological and histopathological examination of Silurus meridionalis, when the disease took place in the catfish farm in Chongqing. There were suffering from the disease and the mortality rate was diseased individuals exhibited traits of hemorrhagic septicemia, and showed symptoms of emaciation, sluggishness, eye exophthalmia, and fin hemorrhages. The viscera symptoms of the diseased fish included ascites, liver swelling, and clear histopathological alterations in spleen and kidney. Histopathological examination revealed hydropic swelling of hepatocytes, tumidity in lymphocytes in spleen. One strain of a bacterial species was isolated from liver, kidney and spleen of diseased southern catfish with typical septicemia symptom, and was named SCL1. The challenge experiments were carried out with healthy juvenile southern catfish by means of injection with live SCL1 at the concentration of 1.0×10⁹ CFU/mL. All individuals of the catfish injected with SCL1 died in a week, and the symptom of the challenged fish was similar to those of the naturally diseased fish, and the LD₅₀ of SCL1 was calculated as CFU/mL in the 22 g body weight southern catfish, while the catfish injected with 0.65% sterile solution in control group had no signs in 7 d post challenge. Therefore, SCL1 was the pathogenic bacterium strain, which was gram negative, rod-shaped, and the same as , kanamycin, and gentamycin, but resistant to trimethoprim, and . This paper will be helpful to disease control and health management during