Nonalcoholic fatty liver disease (NAFLD), especially nonalcoholic steatohepatitis (NASH), is a disease that may lead to liver cirrhosis or hepatocellular carcinoma. The number of patients is increasing steadily and the pathology is diverse. Effective treatment is still mainly focused on diet and exercise therapy. With the advent of the next-generation sequencer, the intestinal flora in NAFLD/NASH is being elucidated. We believe that elevation of endotoxin in the blood caused by intestinal bacterial dysbiosis caused by intestinal permeability enhancement is important for NASH pathology and control of intestinal permeability enhancement has a new possibility for treatment of NAFLD/NASH.