The main objective of the present study was to investigate whether male rats that receive a hypercaloric diet only during the juvenile period (Postnatal Day [PND] 23 to PND65) and a normocaloric diet thereafter exhibit changes in reproductive aspects in adulthood. Body weight gain during the juvenile period and adulthood and the morphology of adipose tissue in adulthood were recorded to determine the effects of the hypercaloric diet. We also evaluated the time of balanopreputial separation, serum testosterone levels, and sexual behavior. Obesity and being overweight are related to an inflammatory process. Therefore, we also examined tumor necrosis factor α (TNF-α) levels in adulthood. Compared with the control group that received only the normocaloric diet, the hypercaloric diet group exhibited an increase in body weight on PND65 and PND90, impairment of sexual behavior, an increase in the number of large adipocytes relative to small cells, a decrease in testosterone levels, and an increase in plasma TNF-α levels. The hypercaloric diet during the juvenile period caused the rats to become overweight, although they were subsequently fed a normocaloric diet until adulthood. The hypercaloric diet resulted in reproductive impairment, reflected by a reduction of sexual behavior, low serum testosterone levels, a reduction of sexual organ weight, and an increase in TNF-α levels.