Mechanical bowel preparation (MBP) for elective colorectal surgery has been practiced as a clinical routine for many decades. However, earlier randomized clinical trials (RCTs) and meta-analyses suggest that MBP should be abandoned before colorectal surgery because of the futility in reducing postoperative complications and motility. The new published results from three RCTs comparing MBP with no MBP in colorectal surgery in 2010 make the updating of systemic review and meta-analysis necessary. The aim of this study was to estimate efficacy of MBP in prevention of postoperative complications for elective colorectal surgery. A literature search was performed mainly in electronic database including Cochrane Library, EMBASE, and MEDLINE. The inclusion criteria were randomized clinical trials comparing MBP with no MBP before colorectal surgery. Septic complications, reoperation, and death were recorded as primary and secondary outcomes. The meta-analysis was conducted according to the QUOROM statement. Fourteen RCTs were included in our analysis with a total number of 5,373 patients: 2,682 with MBP and 2,691 without. Comparing with no MBP for elective colorectal surgery, our study showed that MBP had not reduce any postoperative complications when concerning anastomotic leak [odds ratio (OR) 95% confidence interval (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]. No evidence was noted supporting the use of MBP in patients undergoing elective colorectal surgery. MBP should be omitted in routine clinical practice.