Abstract: Siniperca chuatsi carrying heavy infections of Hebesomea Violentum in the gut were obtained from Liangzi Lake, Hubei Province. For light microscopical examination, the gut were fixed overnight in MFAA (Mathanol∶Formalin∶Acetic acid=85∶ 10∶ 5). After embedding in Histowax, the tissues were serially sectioned at 5μm and stained with May-Grünwald Giemsa using standard techniques. For transmission electronic microscopical examination, small pieces of gut with attached parasites were immersed in ice-cooled fixative and minced in approximately 2mm 3 pieces and then they were fixed in 2.5% glutaraldehyde in phosphate buffered saline (PBS; 0.1 M; pH 7.2) for 4 hours at 4℃ and postfixed for 1h in 1% osmium tetroxide in the same buffer at 4℃, and embedded in Epson-812. Semithin sections were stained with 1% aqueous solution of toluidine blue to select the most suitable areas. Ultrathin sections were double-stained with uranil acetate and lead citrate, and observed in a JEOL JEM-1230 electron microscope at 80kV. The parasite-induced histopathology was related to the penetration of H. violentum proboscis in the intestine wall. The host responded to the parasites with connective tissue hyperplasia and with an infiltration of leukocytes, predominantly eosinophilic granulocytes. Eosinophils were accumulated in the epithelium and lamina propria of the infected gut and some adhere to the parasite tegument and proboscis attachment. These eosinophils were subdivided into immature eosinophils, mature eosinophils and degranulating eosinophils. Fibre cells, fibroblast cells, and eosinophils were orderly distributed at the interface of the parasite-host. In addition, H. violentum elicits the formation of nodule in tunica propria. These nodules comprised a tri-layered structure to wrap the H. violentum. Tissue cava infiltrated by host cells were observed in the lamina propria and they are presumed to be the degenerated nodules.