Purpose: To examine the effects of Tai Chi exercise (TCE) on muscle strength, flexibility of low extremities, postural balance and cognition in patients with Parkinson disease (PD). Method: A nonequivalent control-group pre and post-test design was used. Of the 30 participants 15 were assigned to the experimental group and 15 to the control group. The experimental group participated in 8 weeks of TCE which included one day of exercise with instructor on site and 3 days of self-exercise at home guided by a videotape. Results: The 8 weeks of TCE were found to be significantly effective in enhancing strength of low extremities, flexibility of ankles and shoulders, time of tandem stand with eye closed and level on the K-MMSE (Korean mini mental state examination). Conclusion: These results suggest that TCE has positive effects on physical fitness and cognition in patients with PD. Research over an extended period with the TCE intervention is recommended to identify further effects.