The purpose of the present study was to analyze the efficacy of group counseling conducted in Korea using a method of meta-analysis. For this analysis, 260 doctoral dissertations and master theses were examined and finally 198 studies were selected for the meta-analysis. The selected studies were conducted in Korea from 1990 to 1999 and applied pre-post between group design, which means they were selected because they are controlled studies. From each article, abstract section and result section were used as data. Because many of the studies measured more than one dependent variables, 1,333 effecct sizes were calculated and used for further analyses. These effect sizes were analyzed ~lated to a variety of variables which were classified into three categories: ®A.characteristics of group members(age, need for help), ®Echaracteristics of the group treatment(theoretical approach, goals and focus, structure of program management, number of sessions, length of a session, group size), ®Emethodological issues(length of follow-up measures, random assignment). Major results are as followings: (1)Overall mean effect size of group counseling outcomes was 0.99, and the mean effect size of six-month follow-up was 0.81. The results show that the group counseling treatments conducted in Korea were highly effective and the effects lasted at least for six months; (2)The effect sizes of the various approaches ranged between 0.54 and 1.75 and various group focus ranged between 0.52 and 1.58; (3)Structured group program conducted with a marathon session was more effective than other types of group program management; (4)The mean effect size of the clients who needed treatment was larger than that of pseudo-clients who did not really need treatments; (5)The mean effect size of the studies in which random assignment was applied was larger than non-random assignment. This study is the first, comprehensive meta-analysis on a large scale of research in group counseling outcome conducted in Korea, so the results may give informative data to internationally comparative studies as well as domestic studies.