ObjectiveTo systematically review the efficacy of Roux-en-Y gastric bypass for obesity and its comorbidities. MethodsSuch databases as PubMed, EMbase, The Cochrane Library (Issue 11, 2013), CBM, CNKI, VIP and WanFang Data, etc. were electronically searched from inception to November 2013, for including all studies on Roux-en-Y gastric bypass for obesity and its comorbidities. According to inclusion and exclusion criteria, two reviewers independently screened literature, extracted data, and evaluated methodological quality of included studies. And then meta-analysis was performed using RevMan 5.3 software. ResultsA total of 25 before and after self-control studies involving 2 966 cases with overweight or obesity were included. The results of meta-analysis showed that:after Roux-en-Y gastric bypass operation, the patients had significant reduction in BMI (MD=-16.40, 95%CI-17.42 to-15.38, P < 0.000 01), type 2 diabetes mellitus prevalence (RR=0.23, 95%CI 0.17 to 0.31, P < 0.000 01), and hypertension prevalence (RR=0.34, 95%CI 0.26 to 0.43, P < 0.000 01); besides, fasting glucose, blood pressure and serum lipid levels obviously decreased (P < 0.000 01). ConclusionRoux-en-Y gastric bypass for obesity patients is effective in reducing weight loss, type 2 diabetes mellitus incidence and cardiovascular disease incidence. Due to the limitation of the design of the included studies, the conclusion needs to be verified by further conducting high quality randomized controlled trials with large sample-size.