Background What benefits and toxicities patients acquire from the use of bevacizumab combined with first-line chemotherapy remains controversial.This study was performed to evaluate the efficacy and safety of first-line chemotherapy plus bevacizumab in patients with metastatic colorectal cancer (mCRC).Methods Several databases,including PubMed,Embase,and Cochrane Library,were searched up to April 30,2013.Eligible studies were only randomized,controlled trials (RCTs) with a direct comparison between mCRC patients treated with and without bevacizumab.Overall risk ratio (RR),hazard ratio (HR),odds ratio (OR),and 95％ confidence intervals (CO were calculated employing fixed or random-effects models depending on the heterogeneity of the included trials.Results Six RCTs,including 1582 patients in chemotherapy plus bevacizumab group and 1484 patients in chemotherapyalone group,were included.Overall,the addition of bevacizumab to first-line chemotherapy increased overall response rate (ORR) by 4.5％,prolonged both progression-free survival (PFS) and overall survival (OS),and increased the rate of total Grades 3 or 4 adverse events (G3/4AEs) by 6.9％.Significant differences were found in ORR (RR=1.22 (95％ CI 1.01-1.46),P=0.03),PFS (HR=0.60 (95％ Cl 0.47-0.77),P ＜0.0001),OS (HR=0.83 (95％ Cl 0.70-0.97),P=0.02),and any G3/4AEs (OR=1.56 (95％ Cl 1.29-1.89),P ＜0.00001).Conclusion Bevacizumab is a valuable addition to the current first-line chemotherapy regimens used in patients with mCRC,because of conferring a significant improvement in ORR,PFS,and OS,even though it increased adverse events.