Social work professionals experience high levels of burnout, emotional exhaustion, and secondary traumatic stress (STS). This paper reports the findings of a pilot test of the Burn-Not-Out programme that aimed to reduce social workers' burnout, STS, and depressive symptoms and to enhance compassion satisfaction (CS), using the mixed methods evaluation methodology. Hong Kong social workers participated in the programme between December 2023 and March 2024 and completed pre- and post-programme self-administered online surveys including the Professional Quality of Life (ProQOL) and Patient Health Questionnaire (PHQ-9), healthy alongside self-constructed questions on boundary setting, and post-programme online focus group discussions. The results from 94 paired surveys revealed a concerning mental health profile of the participants at baseline, and, after programme participation, there were statistically significant reductions in burnout (Cohen's d = 0.73) and depressive symptoms (Cohen's d = 0.57) among the participants. The participants in the focus group reported that they valued the programme's emphasis on healthy boundaries, one-on-one coaching, and the sense of being cared for, which contributed to their mental health improvement. This study highlights the urgent need for more research on the role of psychological capital in social workers' resilience and calls for more empirical systemic interventions that can promote social workers' mental wellness, with sustainable policies that ensure manageable workloads and adequate workplace support.