Objective: The goals of the meta-analysis were to investigate the overall effectiveness of cognitive behavioral group therapy (CBGT) for depression and relapse prevention in depression from 2000 to 2010, and to investigate how the variables (episode, residual symptoms, group size, control group, group manual, therapist experience, therapy frequency, session length, and take-home assignment) of a CBGT study could affect the effect size. Method: This study collected actual study designs sought of CBGT for depression published from 2000 to 2010. These studies were then cross-referenced using Medical Subject Headings (MeSH) with the following keywords: group therapy, cognitive therapy, cognitive behavioral therapy, cognitive behavioral group therapy, psychotherapy, depression, relapse, and recurrence. The quality of the studies was evaluated using Cochrane Collaboration Guidelines. The effect size of CBGT on depression and relapse prevention in depression used the formula devised by Hedges and Olkin (1985). Results: The study investigated the results of 32 studies on the effect of CBGT for depression. The CBGT had an immediate (g = -0.40) and continuous effect over 6 months (g = -0.38), but no continuous effect after 6 months (g = -0.06). The CBGT lowered the relapse rate of depression (RD = 0.16). Variables significantly different from each other in terms of immediate effect were: CBGT versus usual care, therapy sessions lasting longer than 1 hour, and take-home assignments. Preintervention severity of depression and patient turnover rate were found to be significantly related to the size of the immediate effect. The relapse rate after 6 months was significantly related only to "participants have no residual symptoms/participants did not mention residual symptoms." Conclusions: Researchers and clinicians should take note that CBGT had a moderate effect on the level of depression and a small effect on the relapse rate of depression. The results of this study suggest that the patient should receive a course of therapy at least every 6 months.