This study aimed to evaluate Thai Buddhism-based Mindfulness (TBbM) feasibility based on recruitment and retention rates and to obtain preliminary data regarding changes (effect sizes) in pain severity and other outcomes when comparing control to intervention participants following TBbM use.A randomized controlled trial was conducted in the Outpatient Department at Sawanpracharak Hospital, Thailand, from April 2018 to February 2019. Seventeen participants completed the pretest and posttest. Both groups (control group [n = 10] and intervention group [n = 7]) received usual care and watched a 25-min educational video about cancer pain. The intervention group participated in a 3-day mindfulness training program at a Buddhist temple and continued practicing at home for 8 weeks. Data were collected at baseline and at 1 and 2 months postintervention.One-hundred and thirty-five participants met the eligibility criteria; 112 (82%) declined to participate and 6 of 23 (26%) were lost to follow-up/dropped out. Control and intervention participants had an average age of 44 (± 8.77) and 56 years (± 7.41), respectively. When compared to the control group, the TBbM participants reported no statistically significant improvements in pain or other outcomes. While not statistically significant, the effect size indicated that pain did improve in the TBbM group (Cohen's d = 0.41).Given the suboptimal recruitment and retention rates, modification of the intervention is warranted. Further, our findings suggest that the intervention had a moderate effect on pain. To evaluate efficacy, future adequately powered studies are needed to test a more feasible TBbM intervention.