Obesity is characterized by abnormal or excessive fat accumulation, which leads to the development of metabolic syndrome. Because oxidative stress is increased in obesity, antioxidants are regarded as suitable agents for preventing metabolic syndrome. Here, we examined the impact of cranberry, which contains various antioxidants, on metabolic profiles, including that during the progression of non-alcoholic fatty liver disease (NAFLD), in high-fat diet (HFD)-fed C57BL/6 mice. We observed that oxidative stress was diminished in mice that were fed HFD diets supplemented with 1 and 5% cranberry powder as compared with that in HFD-fed control mice. Notably, from 1 week after beginning the diets to the end of the study, the body weight of mice in the cranberry-treatment groups was significantly lower than that of mice in the HFD-fed control group; during the early treatment phase, cranberry suppressed the elevation of serum triglycerides; and adipocytes in the adipose tissues of cranberry-supplemented-HFD-fed mice were smaller than these cells in HFD-fed control mice. Lastly, we examined the effect of cranberry on NAFLD, which is one of the manifestations of metabolic syndrome in the liver. Histological analysis of the liver revealed that lipid-droplet formation and hepatocyte ballooning, which are key NAFLD characteristics, were both drastically decreased in cranberry-supplemented-HFD-fed mice relative to the levels in HFD-fed control mice. Our results suggest that cranberry ameliorates HFD-induced metabolic disturbances, particularly during the early treatment stage, and exhibits considerable potential for preventing the progression of NAFLD.