Introduction The benefit of mechanical bowel preparation (MBP) before open colon surgery has been debated over the last decade. The aim of this randomized controlled trial was to evaluate the effect of MBP on the outcome of patients who underwent elective laparoscopic colectomy. Methods Patients who were scheduled to undergo elective laparoscopic colon resection with primary anastomosis were randomly allocated to a preoperative MBP group (either two bottles of sodium phosphate or 2‐L polyethylene glycol) or a no‐MBP group. Anastomotic leakage and other complications such as surgical‐site infection and extra‐abdominal complications were recorded postoperatively. Results In this study, 122 patients were recruited and randomly allocated to the MBP group (n = 62) or the no‐MBP group (n = 60). Demographic and clinical characteristics were not significantly different between the two groups. The rate of abdominal complications, including anastomotic leak and surgical‐site infection, was 16.2% in the MBP group and 18.3% in the no‐MBP group (P = 0.747). Anastomotic leakage occurred in four patients (6.5%) in the MBP group and in two patients (3.3%) in no‐MBP group (P = 0.680). About 29% of patients in the MBP group still had either liquid or solid content in the bowel. No significant difference was found between the length of hospital stay in the MBP group and the no‐MBP group (9.0 ± 2.9 vs 8.4 ± 1.9 days, P = 0.180). Conclusions Elective laparoscopic colectomy without MBP is safe and offers acceptable postoperative morbidity.