Objective To assess the effectiveness of bariatric surgery for obese type 2 diabetes mellitus (T2DM) in Mainland China. Methods Such databases as the Cochrane Central Register of Controlled Trials (Issue 2, 2012), MEDLINE (1990 to February 2012), EMbase (1990 to February 2012), CBM (1990 to February 2012), CNKI (1990 to February 2012), WanFang Data (1999 to February 2012) and VIP (1996 to February 2012) were searched, and the references of the included literature were also retrieved. The studies were screened according to the predefined inclusion and exclusion criteria, the data were extracted, the quality was evaluated, and then the meta-analysis was performed using RevMan 5.2 software. Results A total of 6 controlled before-and-after studies involving 100 patients were included. The overall quality of all literature was as low as grade C. The results of meta-analysis showed that the following indexes after operation obviously decreased than before: 1-month postoperative fasting plasma glucose (MD= –2.27, 95%CI ?4.12 to ?0.42, P=0.02), 6-month postoperative fasting plasma glucose (MD= ?2.73, 95%CI ?2.91 to 2.56, Plt;0.000 01), and 6-month postoperative glycated hemoglobin (SMD= ?1.97, 95%CI ?2.98 to ?0.96, P=0.000 1), and the differences were statistically significant. The sensitivity analysis indicated the results of meta-analysis were credible and stable, but the funnel-plot analysis displayed publication bias might exist in the included studies. Conclusion Current studies show that bariatric surgery is effective for obese T2DM patients in mainland China. However, due to small sample size and low methodological quality of the included studies, its effect has to be proved by high quality, large sample, and long follow-up studies.