Purpose: This study compared Cognitive-Behavioral Therapy (CBT), Mindfulness-Based Cognitive Therapy (MBCT), and Activity-based Supportive Counselling (treatment-as-usual; TAU) for reducing delinquency, psychological risk factors, mental health symptoms, and improving the quality of life among at-risk youths in Hong Kong outreaching social services. Methods: In this quasi-experimental study, non-custodial youths with delinquency and mental health issues underwent eight sessions of CBT ( n = 24), MBCT ( n = 30), or TAU ( n = 61). Results: Dependent-sample t-test showed CBT reduced mental health symptoms and delinquency. TAU reduced mental health symptoms and improved quality of life. MBCT resulted in no significant change. Time x group ANCOVA underscored TAU in improving quality of life. Hierarchical linear regression showed decreases in delinquency and mental health symptoms mediated by decreases in psychological risk factors. Discussion: Results suggest that outreaching social service agencies in Hong Kong could enhance their intervention by augmenting the sports and leisure activities of TAU with structured CBT programs.