BACKGROUND: Self-compassion is a psychological skill associated with good mental health and adjustment to illness in the second half of life, but to date, few self-compassion-based interventions have been developed specifically for use in midlife and older adult cohorts. The purpose of this study was to develop and test the feasibility of a 4-week group self-compassion-based intervention designed to improve self-report and biological markers of well-being in midlife and older adult patients living with chronic illness. METHODS: Treatment development drew on existing literature, expert input, and qualitative interview data. Eight patients in outpatient treatment for a chronic illness were recruited from a rehabilitation hospital (during September and October 2017 and again during February and March 2018) to test feasibility. Participants attended a 1-hour group self-compassion-based intervention once per week for 4 weeks. Feasibility was assessed on 6 domains. Measures of well-being and heart rate variability (HRV), an index of nervous system functioning, were also collected. RESULTS: Recruitment was feasible and occurred within the expected time frame. Attendance at sessions was high (84.4%), with no dropouts. Participants found that the intervention was acceptable, rating sessions as enjoyable (6.8/7) and relevant to daily life (6.6/7). There were no adverse events. Secondary analysis revealed pre-post improvements for some well-being outcomes, such as a significant reduction in depressive symptoms (Hedges\' g = -1.18, 95% CI, -0.18 to -2.16). CONCLUSIONS: A 4-session group self-compassion-based intervention was found to be feasible and acceptable to midlife and older adult patients in treatment for a chronic illness. A larger, randomized pilot trial is needed to explore the efficacy of this intervention. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry (ANZCTR) identifier: ACTRN12619000709145鈥?