The aim of this review was to update and critically evaluate the evidence from randomised clinical trials (RCTs) of tai chi for patients with type 2 diabetes mellitus (T2DM). Twelve databases were searched by August 2014. Fifteen RCTs met all of the inclusion criteria. One RCT compared the effects of tai chi with sham exercise and failed to show the effectiveness of tai chi on fasting blood glucose (FBG), or HbA1c. The other four RCTs tested the effects of tai chi compared with various types of exercise and the meta-analysis failed to show an FBG-lowering effect. Five RCTs compared the effects of tai chi with an anti-diabetic medication and the meta-analysis showed favourable effects of tai chi on FBG. One RCT showed the positive effects of tai chi plus standard care on HbA1c and FBG compared with standard care alone. Four RCTs compared the effects of tai chi to no treatment and the meta-analysis failed to show the positive effects of tai chi on HbA1c. Three RCTs reported superior effects of tai chi on quality of life. In conclusion, the existing trial evidence is not convincing enough to suggest that tai chi is effective for managing patients with T2DM.