The purpose of this study verifies: the relationships between self-leadership and service quality, and mediator effect of the trust in supervisor. In order to verify the relationships and mediator effect, data obtained from 572 workers engaged in medical institutions at Ulsan Metropolitan City were analyzed by using SPSS 12.0, AMOS 5.0. The findings are as follows: First, the relationships between self-leadership and trust in supervisor is positively related. Second, there was also a positive correlation between the trust in supervisor and service quality. Third, the relationships between self-leadership and service quality is positively related. Finally, the trust in supervisor played as a partial mediator on the relationship between self-leadership and service quality. Based on these findings, the implications and the limitations of the study were presented including some directions for future studies.