Objectives. To assess the efficacy and safety of berberine in the treatment of type 2 diabetes mellitus (T2DM). Methods. Randomized trials of berberine compared with lifestyle modification, placebo, and/or oral hypoglycaemics intervention on treating T2DM were included. Study population characteristics and outcome results were extracted independently by two reviewers. Meta-analyses were performed for data available. Results. Fourteen randomized trials, involving 1068 participants, were included in this study. Methodological quality was generally low. Compared with lifestyle modification with or without placebo, the cointervention of berberine and lifestyle modification showed significantly hypoglycaemic and antidyslipidemic response. Compared with oral hypoglycaemics including metformin, glipizide, or rosiglitazone, berberine did not demonstrate a significantly better glycaemic control but showed a mild antidyslipidemic effect. Compared with oral hypoglycaemic drugs, cointerventions with berberine and the same oral hypoglycaemics showed a better glycaemic control. No serious adverse effects from berberine were reported. Conclusions. Berberine appeared to be efficacious for treating hyperglycaemia and dyslipidemia in T2DM. However, the evidence of berberine for treating T2DM should be carefully interpreted due to the low methodological quality, small sample size, limited number of trials, and unidentified risks of bias.