Overfeeding of some waterfowl species results in obesity, which is mainly characterized by a dramatic hepatic steatosis induced by strong accumulation of lipids synthesized from dietary glucose in the liver. In mammals, fructose is known to be able to raise plasma triacylglycerol concentrations significantly; consequently, this may induce obesity. The aim of this study was to assess the effect of partial replacement of dietary glucose provided by corn starch with fructose on metabolism and fatty liver production in the Mule ducks. On the basis of 9.5 kg maize (132,920 kJ) given twice a day for 14 days, a supplementation of 9,800 kJ was provided in form of glucose, sucrose or high fructose corn syrup (HFCS: 50 % glucose, 42 % fructose and 8 % other saccharides). Fatty liver weight in ducks fed with glucose supplementation was 499 +/- 21 g. Sucrose or HFCS supplementation brought about a significant increase in liver weight (+ 18.7 % and + 16.3 % vs. glucose supplementation respectively, p < 0.05). These results suggest that the dietary fructose favors the liver steatosis by increasing hepatic lipogenesis. Postprandial plasma insulin concentrations were similar in ducks fed diets with or without fructose, suggesting that the effect of fructose on liver steatosis is not mediated by insulin.