Resumo. Obesity is a nutritional disorder which has spread across the world mostly due to a more sedentary life style together with an increase in dietary fat and carbohydrate. The scientific literature in the field of obesity shows an extensive amount of clinical and experimental studies dealing with etiopathogeny, intervening problems, prevention and potential intervention. Among them, many studies have examined the impact of obesity in the reproductive field, mainly in the female sphere. The aim of the present study was to investigate whether a hypercaloric diet ingested from weaning interferes with the sexual behavior of adult male rats. Male Wistar rats (at 100 days of age) from the hypercaloric diet group (HD group, n=9) received a hypercaloric diet, containing 4,79 kcal/g and Control animals (n=7) were fed a normocaloric laboratory chow containing 3.78 Kcal/g. For analysis of sexual behavior, one adult male was placed in the observation cage 4 hours after the beginning of the dark phase and 10 min before (for adaptation to the environment) an adult receptive female in natural estrus was introduced. The parameters of sexual behavior (latency and quantity of mounts, intromission and ejaculation), were tape-recorded and registered simultaneously by two investigators, during a 30-min session, with light provided by a 40-watt red lamp. Concerning sexual behavior, the HD animals presented (i) a 70% increase in the amount of incomplete mounts (mounts without intromission), (ii) a 3-fold increase in the latency for the first intromission, (iii) a 27% decrease in the latency for the first pos-ejaculatory intromission, and (iv) a 26% decrease in the frequency of ejaculation. The lower reproductive performance and the tendency of fertility decrease in animals fed a hypercaloric diet from weaning to adulthood, allows us to suggest a negative interference between the ingestion of a hypercaloric diet and these reproductive parameters. Although results obtained from animals should not be directly extrapolated to humans, they may add evidence concerning the deleterious effects of a hypercaloric diet on humans and the species.