Abstract: Vitamin C is an essential micro-nutrient formost fish and plays an important role in immunity and physiology. The deficiency of dietary vitamin C can result in the damage on fish. The study on the deficiency symptom and the sensitive indicator of vitamin C could provide useful information for fish feed industry1 This experimentwas conducted to investigate the effects of dietaryVitamin C levels on growth performance, immune and physiological responses in Chinese longsnout catfish (Leiocassis longirostris G黱ther), which is an high value aquaculture fish in China. Three practical diets containing 38, 364 and 630mg/kg vitamin C were fed to Chinese longsnout catfish (23119 ?158g) for 8 months1 Vitamin C was used in the form of L-ascorbyl-2-polyphosphate1 The results indicated that the Chinese longsnout catfish in 38mg/kg vitamin C groups showed typical vitamin C deficiency symptom: skin color turning darker, spinal deformities and scoliosis, erosion of fins, anaemia1 SGR and the serum lysozyme activities decreased significantly (p p p >0105). The inductive HSP70 in liver was not detected by western2blotting in all groups. In conclusion, serum cortisol and hepatic HSP70 were not the sensitive indicators for vitamin C deficiency symptom, but the serum lysozyme, hepatic SOD activity, hepatic MDA content and the haematological index (red blood cell number and hemoglobin content) were the more reliable makers to indicate the physiological status in Chinese longsnout catfish.