Purpose: To investigate the effect of Tai Chi Chuan (TCC) to improve immune system and decrease pro-metastasis markers in early post-treatment breast cancer survivors. Methods: 130 post-treatment breast cancer survivors were recruited and randomized 1:1 into TCC group and wait-list (control) group. The TCC group practiced for a 60-minutes session once per week, for a total of 52 weeks. 115 forms of Yang-style TCC were taught by a Tai Chi master. Blood samples were taken from each subject and complete blood count was performed. The expressions of NKG2D protein, P-selectin, and vascular endothelial growth factor (VEGF) in plasma were measured. Lymphocyte activity was measured by cell proliferation reagent and ATP assay. Images of lymphocyte colony formation were taken with an inverted microscope. Results: At 52 weeks, TCC group demonstrated a significantly higher WBC (p=0.001) , a significantly higher NKG2D value (p=0.001) and a significantly lower VEGF value (p=0.005) when compared to the wait-list group. However, there was a small, non-significant change for P-selectin values between the breast cancer survivor groups. After 72h incubation, TCC group had a significant increase in lymphocyte proliferation (p=0.001) and greater area of lymphocyte clusters or colonies (p=0.001). Conclusion: The practice of TCC could stimulate tumor immunosurveillance via NKG2D and activate the immune response. VEGF, a marker playing an important role in breast cancer and its metastases, was also reduced in those who practiced TCC. As an alternative for conventional exercise, post-treatment breast cancer survivors may select TCC in their rehabilitation program.