This paper describes the first report of Edwardsiella tarda isolated from hemorrhaged clown knifefish in the Mekong Delta, Vietnam. The study investigated 80 diseased clown knifefish collected from commercial farms in Mekong Delta provinces including Haugiang, Dongthap, and Cantho. Diseased fish showed gross signs of abnormal swimming, exophthalmia with hemorrhages, skin ulcerations, and petechial hemorrhages in fins and body. Internally, ascites with heamoperitoneum, hemorrhaged kidney, light-colored nodules on the liver and splenomegaly were also observed. There were 43 E. tarda isolates obtained from fish samples. Conventional and rapid identification systems, and a further phylogenetical (16S rDNA) characterization were used to identify the pathogen as E. tarda. The experimental challenge was performed in healthy clown knifefish fingerlings (mean weight 15 ± 4 g). The experiement was randomly designed with triplicated intraperitoneal injection with 0.1 ml of E. tarda suspension of 10⁴, 10⁶,10⁸ CFU/ml. Control groups were injected with 0.1 ml sterile saline solution. The results fulfilled Koch's postulates and showed clinical signs similar to those observed in the natural infection, while no mortality was observed in the control groups. The LD₅₀ value for E. tarda isolate at 12 hours was 4.89x10⁵ CFU/ml. The susceptibility of all isolates to 10 selected antibiotics using disk diffusion method was included in the study.