ABSTRACT Background: Previous studies have shown that catastrophizing and avoiding pain increase suffering and disability of patients with fibromyalgia (FM). Acceptance and Commitment Therapy (ACT) has demonstrated good results in the treatment of chronic pain. Method: This study applies a group ACT therapy for women with fibromyalgia, focusing on therapeutic components, such as acceptance, defusion, and personal values. An experimental design with control group was used; 57 women diagnosed with FM participated in this study (25 in the ACT group and 32 in the control group). The ACT group received five intervention sessions. Psychological symptoms, perceived health, mindfulness, catastrophic thinking, and cognitive fusion were evaluated at pre- and post-treatment and at six-month follow-up. Results: The results showed that the ACT group had significantly better results in mental health, social role and functioning, anxiety, depression, somatization, and obsession-compulsion, less catastrophic thinking, and improved capacity for mindfulness at six-month follow-up. Conclusions: The results are discussed in the light of previous interventions.