Treatment for breast cancer produces side effects that diminish functional capacity and quality of life (QOL) among survivors. Tai Chi is a moderate form of exercise that may improve functional capacity, physical activity and oxidative stress. The purpose of this study was to evaluate the effects of regular Tai Chi exercise on malondialdehyde (MDA), SOD and physical fitness (muscle strength, flexibility, flexion, extension, adduction, and abduction). Forty obese women were recruited from a public health center and divided into control (CON: n=20) and trained (EXP: n=20) groups. The Tai Chi exercise group participated in a 12-week (4 times/week) training program. Data were analyzed with T-test. MDA, SOD and physical fitness (muscle strength, flexibility, flexion, extension, adduction, and abduction) were evaluated before and after the Tai Chi program in both groups. There were significant improvements in shoulder flexibility, flexion, extension, abduction, and adduction. However, there was no improvement in muscle strength. There were also significant improvements in MDA and SOD. Based on these results, Tai Chi exercise has been shown to stimulate endogenous antioxidant enzymes and reduce oxidative damage markers. and also be effective in improving physical fitness and QOL. Further study is needed in this area.