Purpose: The purpose of this study was to investigate the effects of a 12-week Tai Chi on the bone mineral density and bone metabolic markers in postmenopausal women Methods: Data were collected from March to July, 2009. Fifty postmenopausal women were recruited for the study. Twenty two women were allocated to experimental group, and 28 to control group. The experimental group underwent Tai Chi exercise twice a week for twelve weeks. The control group was only notified with results of bone mineral density and bone metabolic markers. Bone mineral density was measured by using of DTX-200 (Osteometer MediTech, Hawthorne, CA, USA) at distal radius site and bone metabolic markers were measured by radioimmunoassay method. Collected data were analyzed by t-test, $X^2$-test, and Mann-Whitney test. Results: After 12 weeks of treatment, the Tai Chi group showed a significant difference in bone mineral density compared to control group but no significant effect on osteocalcin and deoxypyridinoline level. Conclusion: Our results suggest that 12 weeks of Tai chi may delay bone loss in postmenopausal women.