Abstract: The study investigated effects of MDA on the growth performance, structure and function of hepatopancreas and intestine of grass carp (Ctenopharyngodon idellus) and evaluated effects between MDA and other products of oxidized fish oil. Five isonitrogenous and isoenergetic diets were prepared with soybean oil, fish oil and different level of MDA for a 72-day experiment. The results indicated that MDA and other products of oxidized fish oil both significantly increased the FCR of grass carp and decreased the SGR and PRR of grass carp (P0.05). Only MDA significantly decreased the LRR (P0.05). Moreover, MDA and other products of oxidized fish oil both significantly decreased the TBA content in serum (P0.05), and increased the content of TC, TG and MDA and the activity of SOD in serum (P0.05). Only MDA significantly increased ALT content and decreased the radio between HDL and LDL in serum (P0.05). MDA and other products of oxidized fish oil both significantly increased the lipid content of hepatopancreas (P0.05) and stimulated the oxidative stress of hepatopancreas. MDA damaged the morphology in hepatopancreas cell and significantly decreased the number of nucleus of hepatopancreas cell (P0.05), which lead to the obviously trend of fibrosis of the hepatopancreas cell. MDA and other products of oxidized fish oil both significantly increased the number of goblet cells in the microvilli (P0.05). To the permeability, serum D-lactic acid and endotoxin significantly increased because of the defect of the tight junction, the hyperplasia and edema of villi. In conclusion, MDA decrease the growth performance of grass carp by regulating the oxidative stress and lipid metabolism. MDA and other products of oxidized fish oil affect the hepatopancreas with different mechanism. Both MDA and other products of oxidized fish oil can mediate the function of intestine.