Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) have been recognized as metabolic disorders characterized by fatty accumulation in the liver without alcohol consumption. The diseases can cause metabolic syndromes, consisting of obesity, diabetes mellitus (DM), dyslipidemia and hypertension. For the treatment of NAFLD/NASH, losing weight by exercise or diet remains the standard treatment, because no effective pharmacological therapy has yet been developed for NAFLD/NASH. Two incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), stimulate glucose-mediated insulin production in pancreatic β cells. Incretin has also been reported to have various extra-pancreatic effects, including the regulation of hepatic glucose production, appetite and satiety, as well as the stimulation of afferent sensory nerves. Therefore, incretin may have potential as a novel therapeutic agent for NAFLD/NASH.