Fear of cancer recurrence (FCR) has a profound negative impact on quality of life (QOL) for many cancer survivors. Breast cancer survivors (BCS) are particularly vulnerable, with up to 70% reporting clinically significant FCR. To the authors' knowledge, evidence-based interventions for managing FCR are limited. Acceptance and commitment therapy (ACT) promotes psychological flexibility in managing life's stressors. The current study examined the feasibility and preliminary efficacy of group-based ACT for FCR in BCS.Post-treatment BCS (91 patients with stage I-III disease) with clinical FCR randomly were assigned to ACT (6 weekly 2-hour group sessions), survivorship education (SE; 6 weekly 2-hour group sessions), or enhanced usual care (EUC; one 30-minute group coaching session with survivorship readings). FCR severity (primary outcome) and avoidant coping, anxiety, post-traumatic stress, depression, QOL, and other FCR-related variables (secondary outcomes) were assessed at baseline (T1), after the intervention (T2), 1 month after the intervention (T3), and 6 months after the intervention (T4) using intent-to-treat analysis.Satisfactory recruitment (43.8%) and retention (94.5%) rates demonstrated feasibility. Although each arm demonstrated within-group reductions in FCR severity over time, only ACT produced significant reductions at each time point compared with baseline, with between-group differences at T4 substantially favoring ACT over SE (Cohen d for effect sizes, 0.80; P < .001) and EUC (Cohen d, 0.61; P < .01). For 10 of 12 secondary outcomes, only ACT produced significant within-group reductions across all time points. By T4, significant moderate to large between-group comparisons favored ACT over SE and EUC with regard to avoidant coping, anxiety, depression, QOL, and FCR-related psychological distress.Group-based ACT is a feasible and promising treatment for FCR and associated outcomes in BCS that warrants testing in larger, fully powered trials.