Tai chi has been claimed to generate beneficial effects with respect to a wide range of diseases. The purpose of this systematic review was to evaluate evidence from randomized clinical trials testing the effectiveness of tai chi for increasing aerobic capacity. Systematic searches were conducted on fourteen electronic databases without restrictions on population characteristics or the language of publication. The outcome measures considered for inclusion were changes in maximal oxygen consumption as a test for aerobic capacity. Five randomized clinical trials (RCTs) met all inclusion criteria. Three RCTs compared the effects of tai chi with no treatment. The meta-analysis failed to show an effect of tai chi on aerobic capacity compared with sedentary controls [n=151, weight mean difference, ml/kg/min, 0.50, 95% confidence intervals -1.14 to 2.15, P=0.55]. Two RCTs compared tai chi with conventional physical exercise including brisk, low intensity and moderate intensity walking, and aerobic exercise. The results show that tai chi was not statistically significantly superior to physical exercise. In conclusion, the existing evidence doe not suggest that regular tai chi is an effective way of increasing aerobic capacity.