This quantitative study examined the relationship between ministry satisfaction and spiritual maturity among adult church volunteers in the Korean Presbyterian church in South Korea (Kosin). It also sought to investigate factors related to volunteers' job satisfaction and their spiritual maturity. Participants included 531 adult small group leaders (males: n = 169; females: n = 362) who were currently involved in the small group ministry in 16 churches of the Kosin denomination. This study utilized the Volunteer Satisfaction Index to measure volunteers' ministry satisfaction, the Spiritual Assessment Inventory to measure their spiritual maturity, and demographic questions. In order to find differences between variables and to seek the correlation between volunteers' spiritual maturity and job satisfaction, the data were analyzed by using t tests, ANOVA tests for parametric data. and Kruskal-Wallis, Mann-Whitney U, and Welsh and Brown-Forsythe tests for nonparametric data. Tukey post-hoc procedures were used when there were statistically significant differences Between groups. Pearson product-moment correlation tests (r) were conducted for correlation. Large effect sizes were found between volunteers' inner convictions of a divine summons and their job satisfaction (total Job Satisfaction: ?[subscript 2] = 0.18; Work Assignment: ?[subscript 2] = 0.25; Participation Efficacy: ?[subscript 2] = 0.22), sense of meaningfulness and satisfaction in ministry and job satisfaction (Participation Efficacy ?[subscript 2] = 0.25; Group Integration: ?[subscript 2] = 0.14), inner conviction of a divine summons and spiritual maturity (Awareness of God: ?[subscript 2] = 0.14; Instability: ?[subscript 2] = 0.018), affirmation of others in the church and two spiritual maturity scores (total Spiritual Maturity: ?[subscript 2] = 0.25; Disappointment: ?[subscript 2] = 0.22), and sense of meaningfulness in ministry and spiritual maturity (total Spiritual Maturity: ?[subscript 2] = 0.26; Impression Management: ?[subscript 2] = 0.19). These findings indicated that a sense of calling was strongly related to volunteers' spiritual maturity as well as their job satisfaction. In addition, there were three relationships with moderate effect sizes: total Job Satisfaction and Awareness of God ( r = 0.402), Work Assignment and Awareness of God (r = 0.421), and Participation Efficacy and Impression Management (r = 0.402). Based on these findings, this study suggested implications for ministry practices. These implications could help church leaders, senior pastors, volunteer staff, and adult church volunteers recognize and develop volunteers' spiritual maturity and job satisfaction by offering various intentional programs or other resources. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]