The endocannabinoidome (eCBome) and gut microbiome play key roles in metabolism and obesity, and oleoylethanolamide (OEA), a lipid mediator within the eCBome, is known to reduce food intake and promote fat oxidation. This study investigated the effects of OEA administration on mice with diet-induced obesity, focusing on hepatic inflammation and mitochondrial function, the endocannabinoidome (eCBome), and the gut microbiome. Mice fed standard (STD) or high-fat (HFD) diets for 18 weeks were treated with either vehicle or OEA. Metabolic, inflammatory, oxidative stress and mitochondrial parameters were assessed, along with intestinal and hepatic levels of eCBome lipids and fecal microbiota and short chain fatty acid composition. In HFD-fed mice, OEA decreased body weight, food intake, and serum and liver inflammatory markers, limiting hepatic and body fat accumulation. OEA improved liver mitochondrial oxidative capacity, lipid metabolism and oxidative stress. It reduced intestinal levels of the endocannabinoid 2-arachidonoylglycerol. Effects on microbiota composition were mostly found in the STD-fed group. However, OEA increased the relative abundance of Akkermansia muciniphila more strongly in HFD-fed mice. These findings suggest that OEA may help counteract obesity-related metabolic dysfunction and inflammation, and gut microbiota unbalance, thus representing a promising candidate for future therapeutic strategies.