Purpose: This randomized study was done to compare the effects of a 6 month Tai Chi exercise and a self-help program on balance, flexibility and muscle strength in women with osteoarthritis (OA). Method: In this experimental study, 82 women with OA recruited from outpatient clinics or community health centers were randomly assigned either to a Tai Chi group or a self-help group. Thirty women (mean age = 62 years) in the Tai Chi group and 39 (mean age = 59 years) in the self-help group completed posttest measures (balance, flexibility, oxygen consumption, abdominal muscle strength, back muscle strength, and grip strength) at 6 months. Results: After the 6 month, Tai Chi participants had significantly greater balance (mean difference = 2.9 vs. 0.9 for the self-help), grip strength (mean difference = 4.6 vs. 0.9 for the self-help), and back muscle strength (mean difference = 4.1 vs. -0.3 for the self-help). However, flexibility, oxygen consumption, and abdominal muscle strength were not significantly different between the groups. Conclusion: Tai Chi increased balance, grip strength and back muscle strength in older women with osteoarthritis compared to the self-help program. Whether these changes improve physical functioning and fall prevention requires further study.