Nonalcoholic steatohepatitis (NASH), a subtype of nonalcoholic fatty liver disease (NAFLD), has a potentially progressive course that can lead to liver cirrhosis. Age is strongly associated with the development and progression of NAFLD/NASH, but the natural history of pediatric NAFLD is still not fully understood. Here, we evaluated the age-related alterations of NASH in 5-, 9- and 13-wk-old male Sprague-Dawley rats that were fed a high-fat and high-cholesterol diet (30% fat, 1.25% cholesterol and 0.5% sodium cholate, w/w) for 9 wk (6 rats/group). Our results showed that the cumulative energy intake, body weight gain and food efficacy during the 9-wk rearing period were highest in the youngest group and lowest in the oldest group. Serologically, almost all parameters including the serum triglyceride and total cholesterol were similar regardless of age. Histopathological findings, such as hepatic steatosis, lobular inflammation and hepatocyte ballooning, were also similar regardless of age, but hepatic fibrosis was more evident in the oldest group. Also, the mRNA expression levels of some fibrogenic, inflammatory, oxidative stress and cholesterol or lipid metabolism-related genes in the liver were highest in the oldest group and lowest in the youngest group, although the difference was not statistically significant. These results indicated that aging is likely associated with the development of NASH. Because the cumulative energy intake and daily food intake/body weight were not similar among groups in the present study, further studies designed with an equivalent daily food intake/body weight among groups are needed in order to interpret the exact nutritional effect.