The study was conducted to detennine the morphological, physiological, biochemical, and pathogenicity of purA gene knocked-out Edwardsiella ictaluri strain (PAM). Culture growth, Gram staining, and biochemical tests showed that the purA gene knocked-out strain PAM had similar phenotypes and biochemical characteristics as the wild-type WT (except for adenine biosynthesis). Catfish individuals injected with WT at 10s cfu/fish, showed 100 percent mortality and dead fish had external and internal lesions consistent with enteric septicemia of catfish in ponds, whereas catfish individuals injected with PAM at 10s cfu/fish was survival after injection for 15 days. The lethal does 50 percent (LD50) of PAM strain was high ( 10 exponent 9 cfu/fish). Research result demonstrated the ability to cause enteric septicemia of PAM was weaker than WT strain. PAM strain was cultured and preserved to detennine immunogenicity capacity on Catra catfish.