The present study aimed to investigate the effect of metformin on the induction of autophagy in the liver and adipose tissues of a mouse model of obesity. C57BL/6J mice were fed a high-fat diet (HFD) for 12 weeks to induce obesity-associated hepatic steatosis, and treated with metformin (150 mg/kg/d) by intraperitoneal injection for the final 4 weeks of HFD feeding. Body weight was recorded weekly, and the food intake of the mice was recorded daily during the treatment period. Liver and adipose tissues were harvested for histological and molecular analyses. The results revealed that metformin significantly reduced body weight without altering food intake in the HFD mice, particularly in the epididymal white adipose tissue (eWAT). Metformin treatment ameliorated HFD-induced hepatic steatosis and serum levels of triglycerides, which was consistent with a marked increase in the expression levels of microtubule-associated protein 1 light chain 3 (LC3) and AMP-activated protein kinase (AMPK) in the liver following metformin treatment. However, metformin suppressed the expression of LC3 in the eWAT without altering the expression of AMPK, compared with that in the HFD mice. In conclusion, metformin reduced the body weight and hepatic steatosis of the HFD-induced obese mice, without altering food intake. The effects of metformin treatment may be attributable to the improved induction of hepatic autophagy and the inhibited induction of adipose tissue autophagy.