Objective To systematically review the effectiveness and safety of coronary artery bypass grafting (CABG) versus percutaneous coronary stent implantation (PCI) in the treatment of patients with unprotected left main coronary artery disease (ULMCA). Methods Databases including The Cochrane Library (Issue 2, 2012), PubMed, EMbase, CBM, CNKI, WanFang Data and VIP were electronically searched from inception to September 2012 for randomized controlled trials on the effectiveness and safety of coronary artery bypass grafting (CABG) versus percutaneous coronary stent implantation (PCI) for ULMCA; References of the included studies were also retrieved. Two reviewers independently screened literature according to the inclusion and exclusion criteria, extracted data, and assessed the methodological quality of the included studies. Then, meta-analysis was performed using RevMan 5.0. Results Four studies were included involving 1 611 cases, of which, 802 cases are in the CABG group, while 809 cases were in the PCI group. The results of meta-analysis showed that: comparing with PCI, CABG significantly reduced the postoperative repeat revascularization rate (OR=0.45, 95%CI 0.31 to 0.66, Plt;0.000 1), but there was no significant difference between the two groups in reducing the myocardial infarction incidence (OR=1.28, 95%CI 0.47 to 3.48, P=0.63), mortality rate (OR=1.36, 95%CI 0.80 to 2.34, P=0.26), and the incidence of major adverse cardio-cerebral vascular events (OR=0.92, 95%CI 0.66 to 1.28, P=0.61). Conclusion This study indicates that CABG is superior to PCI in reducing postoperative rate of target vessel revascularization. But CABG and PCI are alike in reducing myocardial infarction incidence, mortality rate, and the incidence of major adverse cardio-cerebral vascular events. Due to the limited quantity and quality of the included studies, the above conclusion needs to be verified by more high quality RCTs.