Purpose: The purpose of this study was to investigate the effects of Tai Chi exercise program on physical fitness, pain, and self-efficacy in patients with osteoarthritis. Method: A preexperimental research design was applied to 22 subjects who dwelled at a welfare institution in C-city and agreed to participate in this study. The Tai Chi exercise was conducted with a duration of 60 minutes per session twice a week for 9 weeks. Outcome measures were physical fitness($VO_{2}max$, strength, flexibility, foot power, agility, balance), pain, and self-efficacy. Data were analyzed by descriptive statistics and paired t-test. Result: After participating in the Tai Chi exercise program, the subjects showed significant improvements in strength, agility, balance, pain and self-efficacy. But there were no significant differences in $VO_{2}max$, flexibility and foot power. Conclusion: The results showed that Tai Chi exercise would partially improve physical fitness and be effective for pain reduction and self efficacy as well. Further studies are needed to confirm the effects of Tai Chi exercise on physical fitness.