Obesity is a multifactorial disease, where the major factor involved is the consumption of high-fat, high-palatability food. The prevalence of this disease has increased in all age groups, but the increase in children and youth is alarming. Food intake is controlled by brain areas involved in homeostatic and hedonic control, both systems being regulated by the GABAergic nucleus, lateral septum (LS). The LS neurons are regulated by several membrane receptors, where the regulation of food intake in an obese condition by μ-opioid receptor (MOR) has not been previously studied.This work aimed to evaluate the effect of an obesogenic diet in juvenile rats for 6 weeks on MOR gene expression in LS. Sprague-Dawley rats were exposed from postnatal day 21 to postnatal day 62 to chow plus water (control group) or high-fat diet plus sucrose solution (HFD+S group) ad libitum.Our data showed that HFD+S exposure decreased the MOR gene expression in LS of male rats relative to their controls. In contrast, the MOR gene expression was not affected by HFD+S in female rats. These data demonstrate that HFD+S exposure during adolescence modifies MOR gene expression in a sex-specific manner in LS, a key core in food intake. Further experiments are needed to determine whether these changes can affect MOR functionality concerning food intake in obesity.