Obesity is defined as increased mass of adipose tissue, conferring a higher risk of cardiovascular and metabolic disorders such as diabetes, hyperlipidemia, and coronary heart disease. To get a better understanding of the role of a male sex hormone testosterone on obesity, we thus measured the effects of testosterone on white adipose tissue (WAT) mass, adipocyte histology and hepatic lipid accumulation in male castrated (CAST) C57BL/6J mice. Compared to male CAST control mice, testosterone-treated mice had the decreased WAT mass and the increased the number of adipocytes. Especially, histological data showed that the adipocyte size was reduced in a dose-dependent manner and was most effective at dose 150 $mu$g per mouse for testosterone. In addition, the administration of testosterone resulted in the inhibition of hepatic lipid accumulation compared with control mice. Our results suggest that testosterone regulates adipocytes development and hepatic lipid metabolism, resulting in the prevention of obesity in male CAST mice.