Obesity has emerged as a prominent global health concern in recent times, a phenomenon often attributed to the excessive consumption of highly palatable, calorie-rich foods laden with sugar and fat. These diets can modulate certain neural pathways, such as the mesolimbic dopaminergic system of reward, but their potential addictive properties are still unknown although its effects have been widely studied. Additionally, Δ9-tetrahydrocannabinol (THC), the main psychoactive component of cannabis sativa, has been found to have an important orexigenic role and modulating properties over the reward system. Considering this, we conducted a study using two high-fat diets with no added sugar: SOLF (saturated fat) and UOLF (unsaturated fat) in a model of operant self-administration with Skinner boxes following a three criteria protocol: 1) reward seeking behavior, 2) motivation to obtain the reward and 3) compulsivity. Young C57/BL6 mice, both male and female, were subjected to an increasing reinforcement program followed by a progressive ratio session aimed at finding the breaking point and finally, a cue-induced reinstatement session following an extinction phase. Experiments were carried out both in naïve animals and animals treated with THC/saline (5mg/kg, i.p.). We found that both saturated and unsaturated fats induce a potent seeking behavior of the substance, with high compulsivity and a great motivation to obtain the diet. Moreover, we found that THC during the juvenile period modulated these addiction-like behaviors towards SOLF and UOLF.Acknowledgements: Ministerio de Economía y Competitividad (BFU2016-78556R, PID2020-117422RB-C21, PID2020-117422RB-C22), Red de Investigación en Atención Primaria en Adicciones (RIAPAd) (RD21/0009/0020).