This study is to investigate what effects group bible study within a Catholic Church has on the faith maturity and evangelicalism of Catholicism and to what degree it has influence on psychological change of Catholics in the aspect of religious life. In order to achieve this purpose, I considered four hypotheses about changes of mature faith index, religious life, religious orientations, and psychological well-being through Group Bible Study. The total subjects who have participated in group bible study are 330 Catholics. The findings from this study which has been done on group bible study for 10 months are as follows; First, in case that Catholics have joined the Group Bible Study for a certain period, they shows positive changes in Mature Faith Index. Besides, the maturity of vertical themes which are based on religious value or belief is more extinct than that of the horizontal themes on activation of religious community. Secondly, Catholics who have participated in Group Bible Study show positive changes in psychological elements, which means the evident effect of Group Bible Study, and show significant changes in commitment to belief and effort for spiritual maturity. Thirdly, regarding the effects of Group Bible Study on Religious Orientations, significant changes come out in external orientation related to Catholics pride in religious circumstances and in interactional orientation which means activation resulting in personal relationships in religious community. Finally in the aspect of the changes of Psychological Well- Being, the subjects who have been joined group bible study have been consecrated to some degree, but show no significant changes in Psychological Well- Being coming from in- depth mentality.