Few studies have quantified the improvements in motor coordination after Tai Chi (TC) training in Parkinson Disease (PD). Further, given that people with PD have difficulties with balance while performing a secondary task, interventions that involve dual-task components are needed. We investigated whether TC improved their postural control under secondary cognitive/motor task condition in persons with PD. Eleven participants with PD completed the 16-week TC training, and were compared to five non-exercise PD controls. During baseline testing, each participant stood for 10 seconds on a force platform and held a set of two cylinders stacked together. Center of pressure excursion was collected at 360Hz under three task conditions: static (holding objects), secondary cognitive (a digit subtraction while holding objects), and secondary motor (pulling the top cylinder apart). Participants underwent the same baseline tests following the 16-week period. The change score after 16 weeks in Approximate entropy (ApEn) on anteroposterior (A/P) and mediolateral (M/L) directions and 95% confidence ellipse (Area95) were evaluated using independent t-test in each condition. After 16 weeks, TC participants reduced their Area95 (-.05±.57cm2) in static condition when compared to the control group (+.73±.78cm2, p<.05). Change in ApEn in TC participants (A/P: +.12±.35, M/L: -.01±.23) did not significantly differ from the control group (A/P: +.07±.23, M/L: +.10±.23). No significant differences were observed in any of two secondary task conditions. In conclusion, Tai Chi intervention appears to be effective for persons with PD to improve their postural control under cognitively less challenging condition. However, this benefit could not be reflected in postural control while performing a secondary task.