The pathogen Virio harveyi was isolated from the focus of illed Pseudosciaena crocea was infected back to the healthy P．crocea artificially． The challenged fish indicated the typical ulcered syndrome． The blood chemistry parameters were tested．The challenged fish indicated significantly（P<0.01）lower percentages of monocytes,polymorphonuclear neutrophil granulocytes(PMN) and thrombocytes but higher percentages of leucocytes; it differed from the control fish. Significant decreases in total protein, globulin, triacyl glycerol and blood glucoe concentrations were found in the challenged fish compared to the control fish（P<0.01）,with the total protein values at （12.8 ±3.95） g/L and （19.4±4.33） g/L, respectively. Significant increases of alanine aminotransferase（ALT）and aspartate aminotransferase（AST）concentrations were found in the challenged fish compared to the healthy fish（P<0.01）. The concentrations of ALT and AST were （37±5.11） IU/L and （164±47.19） IU/L in the challenged fish, while in the control fish were （28±5.54） IU/L and （117±21.84） IU/L. The results indicated liver and kidney damage， and disturbances in hepatic and osmoregulatory function of P.crocea.Observations by histopathology showed that head kidney and liver of the tested P.crocea were severely damaged and various denaturalization and necrosis. Denaturalization and necrosis emerged in the epithelial cell of renal tubule under electronic microscope. Fatty were accumulated in the cytoplasm of hepatic cells. The serum chemistry parameters determinations was a good inicator of bacterial infection of the challenged fish.