Abstract: The prevalence of obese cats has increased because of over calorie diet and physical inactivity. Obesity has been found to be associated with oxidative stress and Reactive Oxygen Species (ROS). Unfortunately oxidative stress status at the early phase of obesity in high fat fed cats is not well understood. The objectives of this study were (1) To evaluate lipid and glucose metabolism using enzymatic, hormonal and oxidative stress biomarkers at the early obese phase of cats fed on a high-fat diet and (2) To identify rapidly changing variables to use as a diagnostic marker for lipid metabolic disorders in cats. Total 13 domestic female cats were divided into two groups which were fed on control and high-fat diet for eight weeks, respectively. After the feeding period, they were compared in metabolic variables and oxidative stress markers in plasma and tissues. As results, High-fat diet including much long chain fatty acids promoted rapid changes in lipid metabolism, particularly accelerated β-oxidation of fatty acids and oxidative stress in the liver of the cats. G6PD, GPx and SOD were increased in the liver. Insulin resistance was not apparent at the early phase of obesity in cats. Plasma activities of SOD also increased at the early phase of obesity in cats. Remarkable alternation for oxidative stress in liver was observed at the early phase of obesity in cats fed on high fat diet and SOD may be a potential marker of the early phase of obesity in cats.