Recently, the focus of marketing research has changed from transaction marketing to relationship marketing, so exchange between a company and a customer emphasize the long-term orientation. Such a trend is also true in medical service industry because of the increasing competition globalization of medical service industry and increasing expectation of service by the customer. So this research focuses on relationship marketing of the medical service industry. The core concepts of relationship marketing research are the relationship quality and service loyalty. The research model of this research include two main themes. One is that the medical service quality(technical quality, personal quality, physical quality, and order quality) has an effect on the service loyalty(attitudinal loyalty, behavioral loyalty) through the relationship quality(satisfaction, trust). The other is that moderating effects of switching barriers(switching cost, attractiveness of alternatives) between satisfaction and behavioral loyalty, and between trust and behavioral loyalty. Empirical research was conducted for that purposes and the findings are as follows.