<p>To investigate the impact of smartphone-delivered ecological momentary assessment (EMA) as a self-monitoring tool to complement a 6-week group face-to-face delivered multicomponent lifestyle medicine (LM) intervention for improving depressive symptoms. 56 Chinese Hong Kong adults with at least a moderate level of depressive symptoms were randomized to the EMA-supported intervention (LM/S; <i>n</i> = 18), pure intervention (PLM; <i>n</i> = 20), or care-as-usual (CAU; <i>n</i> = 18) groups. Data were collected at baseline, immediate post-intervention, and 3-month follow-up. LM/S only showed significantly greater vigorous physical activity than PLM at Week 19. At Week 7, PLM demonstrated a marginal reduction in depressive symptoms and significant improvements in insomnia symptoms, physical health-related quality of life (QoL), overall lifestyle, nutrition, and stress management compared to CAU, while LM/S improved only environmental health-related QoL. At Week 19, both intervention groups showed large improvements in depressive, anxiety, and insomnia symptoms, environmental health-related QoL, overall lifestyle, and stress management compared to CAU. Additional gains were observed for LM/S in nutrition, spiritual growth, and vigorous activity, and for PLM in physical and psychological health-related QoL, and interpersonal relationships. No significant differences in study attrition and intervention attendance were found between groups. Despite a low EMA compliance of 27.1%, the LM/S exhibited a higher, though not significantly different, full intervention adherence rate (66.67%) compared to the PLM (38.89%). A group-based, multicomponent LM intervention could potentially improve depressive symptoms, and smartphone-delivered EMA might enhance full intervention adherence despite modest compliance. A future adequately powered trial is warranted.</p>