The purpose of this study was to identify the relationship between self-efficacy and adherence of aquatic exercise in patients with chronic arthritis. Subjects were 54 patients with rheumatoid arthritis and osteoarthritis who had participated in the 6-week aquatic exercise program. The results indicated that the relationship between self-efficacy and aquatic exercise adherence in patients with chronic arthritis was statistically significant. A significant difference of self-efficacy was found between adherers and non-adherers and self-efficacy of adherer was higher than that of non-adherer(t=5.21, p=.000). Self-efficacy was significantly associated with the total duration of an aquatic exercise adherence(r=.44, p=.001). Based on these results, self-efficacy was the important factor which affect adherence of aquatic exercise in patients with chronic arthritis. Further study was suggested to identify the relationships among self-efficacy, exercise barrier and other possible factors.