Current behavioral interventions for weight loss in overweight and obesity present problems in maintaining long-term weight loss results. Acceptance and commitment therapy (ACT) could be a suitable approach to promote long-term weight loss. The aim of this pilot study is to evaluate the efficacy of an ACT-based intervention on body weight change at the end of the intervention and after a 9-month follow-up, in addition to analyzing the effects of the intervention on several variables of interest. Nine women (Mage= 44.11 years; SD= 5.82) attended a group intervention of 10 weekly sessions, addressing contents of eating habits, physical activity, and ACT. At the end of the intervention, the average weight loss was 2.8%, and after a 9-month follow-up, it was 3.9%. Based on the results, it can be concluded that the study provides evidence in favor of the suitability of ACT to help promote weight loss.