Aim: A double-blind randomised controlled study was conducted to compare the effect of magnesium oxide (1 g 12-hourly) with placebo given within an evidence-based multimodal rehabilitation programme on gastrointestinal recovery, pain, mobilisation and hospital stay after open colonic resection. Method: Of sixty two potentially eligible patients, thirteen were excluded leaving 22 in the magnesium oxide group and 27 in the placebo group. The main outcome measure was time to normalization of bowel function. Secondary outcome measures included post operative nausea, vomiting, pain, fatigue, mobilisation and length of postoperative hospital stay. Results: The median times to first flatus and defaecation in the laxative and placebo groups were 18.0 vs. 14.0 hours and 42 vs. 50 hours (p>0.15). Early intake of liquids, protein drinks and solid food, nausea and vomiting, pain, fatigue and mobilisation were similar in the groups (p>0.3). The median postoperative hospital stay was three days in both groups (p>0.65). Conclusion: Magnesium oxide does not enhance the recovery of gastrointestinal function within the context of an evidence-based multimodal rehabilitation programme after open colonic surgery.