Objectives : Many researchers in western societies raised questions on methodological limitations of randomized controlled trial (RCT) for studying Complementary and Alternative Medicine (CAM), and they have tried to find alternatives to RCT. Some of them recently have interest in health service research as one of the alternatives. Discussing the significance of health services research in CAM studies will be helpful to guide the researchers in Korea who are also interested in developing an appropriate research methodology for traditional Korean medicine. Methods : Previous studies on methodological issues of studying CAM and health service researches published in western societies until 2009 were searched mainly from Pubmed. The definition, main research domains, and research methods of health service research and the significance of it for researches on CAM were summarized. Results & Conclusions : Health service researches are important in two aspects. First, health service researches evaluate the actual practice of CAM, including the individualized diagnosis as well as treatment and interaction between practitioners and patients. Second, when evaluating the outcomes, they put an emphasis on subjective evaluation by patients as well as objective evaluation by doctors. Thus, it can reflect the treatment goals of CAM which is improving the overall quality of life and the physical and psychological health. Therefore, health services researches such as descriptive studies, qualitative studies, outcomes studies including economic evaluation, and whole systemic research should be more utilized in order for studying traditional Korean medicine.