Purpose:The purpose of this study was to investigate the effects of peer mentoring program on physical activity, knee joint function, self-care agency and social support, which are health conservation elements in elderly women with osteoarthritis. Methods: This study used a quasi-experimental research design. It is a pretest-and-post 1, post 2 test design of a non-equivalent control group. The subjects were elderly women aged over 65 who were diagnosed with osteoarthritis. A total of 60 patients (experimental group 30, control group 30) who registered with the Senior Welfare Center in City G and in Region D participated in this study. The data were collected from June 29th to September 4th, 2015. The collected data were analyzed with x 2 test, Fisher's exact test, independent t-test and repeated measurement ANOVA. Results: The experimental group showed a greater increase in physical activity, knee joint function, self-care agency and social support than the control group. Conclusion: The results indicated that the peer mentoring program is effective in increasing physical activity, knee joint function, self-care agency and social support of elderly women with osteoarthritis.