ObjectiveTo determine the benefits and harms of mechanical bowel preparation(MBP) in elective colorectal surgery. MethodsCochrane systematic evaluation was used to search through Cochrane libraries of clinical comparative trials, PubMed, Embase, Cancer Lit, and the Chinese BioMedical Literature on disc. The quality of literatures was independently evaluated and cross-checked by two evaluators, indicator for assessment including anastomotic leak, overall surgical site infection(SSI), extra-abdominal septic complications, wound infections, reoperation or second intervention rate, and death. The results were analysed with RevMan 5.1 software. ResultsFourteen RCTs were included in this analysis with a total number of 5 373 patients. Comparing with no MBP for elective colorectal surgery, the study results showed that MBP had not reduce any postoperative complications when concerning anastomotic leak[OR(95% CI), 1.08(0.82-1.43);P=0.56];overall SSI[OR(95% CI), 1.26(0.94-1.68);P=0.12];extra-abdominal septic complications[OR(95% CI), 0.98(0.81-1.18);P=0.81];wound infections[OR(95% CI), 1.21(1.00-1.46);P=0.05];reoperation or second intervention rate[OR(95% CI), 1.11(0.86-1.45);P=0.42], and death[OR(95% CI), 0.97(0.63-1.48);P=0.88]. ConclusionNo evidence supporting the use of MBP in patients undergoing elective colorectal surgery. MBP should be omitted in routine clinical practice.