Background: Emotional distress often causes patients with cancer and their family caregivers (FCGs) to avoid end-of-life discussions and advance care planning (ACP), which may undermine quality of life (QoL). Most ACP interventions fail to address emotional barriers that impede timely ACP.; Aim: We assessed feasibility, acceptability, and preliminary effects of a mindfulness-based intervention to facilitate ACP for adults with advanced-stage cancer and their FCGs.; Design: A single-arm pilot was conducted to assess the impact of a 6-week group mindfulness intervention on ACP behaviors (patients only), QoL, family communication, avoidant coping, distress, and other outcomes from baseline (T1) to post-intervention (T2) and 1 month later (T3).; Participants: Eligible patients had advanced-stage solid malignancies, limited ACP engagement, and an FCG willing to participate. Thirteen dyads (N = 26 participants) enrolled at an academic cancer center in the United States.; Results: Of eligible patients, 59.1% enrolled. Attendance (70.8% across 6 sessions) and retention (84.6% for patients; 92.3% for FCGs) through T3 were acceptable. Over 90% of completers reported high intervention satisfaction. From T1 to T3, patient engagement more than doubled in each of 3 ACP behaviors assessed. Patients reported large significant decreases in distress at T2 and T3. Family caregivers reported large significant improvements in QoL and family communication at T2 and T3. Both patients and FCGs reported notable reductions in sleep disturbance and avoidant coping at T3.; Conclusions: The mindfulness intervention was feasible and acceptable and supported improvements in ACP and associated outcomes for patients and FCGs. A randomized trial of mindfulness training for ACP is warranted. The study is registered at ClinicalTrials.gov with identifier NCT02367508 ( https://clinicaltrials.gov/ct2/show/NCT02367508 ).