Treatment of breast cancer can significantly diminish functional capacity in patients months and even years after the completion of treatments. Tai chi chuan (TCC) is a moderate form of exercise that may be an effective therapy for improving functional capacity among breast cancer survivors. We sought to provide pilot data comparing the efficacy of TCC and psychosocial therapy (PST; physical activity control) for improving functional capacity among breast cancer survivors post treatment. Twenty-one women who had completed treatment of breast cancer were randomized to receive TCC or PST 3 times/wk for 12 weeks. Functional capacity was assessed at baseline and at 12 weeks. The TCC group demonstrated significant improvement in functional capacity (specifically aerobic capacity, muscular strength, and flexibility) whereas the PST group showed significant improvement in flexibility only. These data suggest that TCC may be an efficacious intervention for enhancing functional capacity among breast cancer survivors and may support the need for larger randomized, controlled clinical trials to further elucidate these relationships.