OBJECTIVES: With the development of online technology and the increase in real-world needs, conducting psychotherapy on online platforms has become a popular trend. The present study followed the schedule and content of Mindfulness-based Cognitive Therapy (MBCT), and only changed the treatment format (from offline to online) to investigate the effectiveness of online group MBCT for Chinese outpatients with depression. METHODS: The study used before-and-after controlled design, and included 88 depressed outpatients, of which 75 formally underwent a 10-week online group MBCT. The 24-item Hamilton Depression Scale (HAMD-24), Hamilton Anxiety Scale (HAMA), Self-Depression Rating Scale (SDS), Mindful Attention Awareness Scale (MAAS), and Self-Acceptance Questionnaire (SAQ) were administered to patients one week prior to treatment, the fifth week of treatment, and the tenth week of treatment. Repeated-measures data were processed using linear mixed-effects models. RESULTS: 75 patients (85.23 %) attended >4 sessions, 44 of whom were taking psychotropic medication during treatment. HAMD-24 and HAMA scores decreased significantly in both medicated and unmedicated patients (w10 < w1, p < 0.05). HAMD-24 and HAMA scores declined more rapidly in patients taking medication, with significant decreases in the fifth week (w5 < w1, p < 0.05). The remarkable effectiveness of treatment (HAMD-24 score reduction >50 %) was >30 %, but there were no significant changes in patients' SDS, MAAS, or SAQ scores. CONCLUSIONS: This study supports the effectiveness of online group MBCT for outpatients with depression and the adherence of depressed patients to participate in online group MBCT was high.