A central issue in the understanding of the pathogenesis of nonalcoholic fatty liver disease is the problem of the underlying mechanisms which are not fully understood. In the setting of excessive central adiposity, insulin resistance is the major underlying cause of fat accumulation in hepatocytes. Because of the difficulties with human trials, several animal models have been developed for this purpose mainly characterized as follows: genetically disturbed or murine fatty liver, methionine- choline deficient diet fed or murine steatohepatitis, and high-fat or sucrose diet fed models. Although these animal models have provided useful information,none of them accurately reflect genetic, metabolic and biochemical characteristics of the human disease.