The aim of this investigation was to evaluate the efficacy of Alisma orientalis methanolic extract (AOME) on the experimental nonalcoholic fatty liver disease (NAFLD) induced by high-fat diet. Rats were fed with high-fat diet for six weeks and then gavaged the AOME for another six weeks. Typical pathological symptoms of NAFLD occurred in the high-fat diet rats. Administration with the AOME (150,300 and 600 mg kg (-1)) markedly decreased the serum and liver lipids; the high level of fasting serum glucose was reduced and insulin resistance was improved. The AOME treatment was also helpful in preventing the oxidative stress by lessening lipid peroxidation and activating antioxidant enzymes. Markers of the liver injury, aminotransferase abnormalities and hepatomegaly were improved and morphological changes, such as liver steatosis, mixed inflammation and collagen deposition, were lessened in rats treated with the AOME. These results suggested that the AOME showed hepatoprotective effects on NAFLD and may be a potential clinical application for treatment of this chronic liver disease.