In order to understand the occurring and developing regularity and the essence of the Pseudodactylogrus bini disease in European eel (Anguilla anguilla）researches of the symptom, epizootic and gill histopathology of diseased European eel were made. The main symptoms of the diseased eel were abnormal swimming, unusual respiration, gill edema and mucus increasing. Although Pseudodactylogrus bini disease of European eel also occurred in winter, it mainly occurred in the end of spring, summer and the beginning of autumn when water temperature was above 26°C. There were five types in histopathological changes of gill. The first change was hyperplasia of epithelial calls in secondary gill lamellae which caused the fusion with the adjacent secondary gill lamella; The second was hyperplasia of mucous cells in secondary gill lamellae which also caused the fusion with the adjacent secondary gill lamella; The third was that secondary gill lamellae were edema but epithelial calls in secondary gill lamellae were not edema and detached from capillaries. The structure of the secondary gill lamellae disappeared as the epithelial cells were necrotic and lysis at the late stage; The fourth was that both secondary gill lamellae and epithelial cells were edema, and the layer of epithelial cells detached from capillaries. The structure of the secondary gill lamellae disappeared due to the necrosis of epithelial cells; The last one was formation of gill lamellae aneurisms which were club-shaped and global due to the dilatation and congestion of capillaries. All above five types in histopathological changes of gill influenced the respiratory function of diseased European eels, which reduced their growth or resulted in their death when the disease was severe.