Post-operative ileus (PI) is an inevitable adverse consequence of abdominal surgical procedures. We performed a randomized study of the effects of the herbal medicine dai-kenchu-to (DKT) on 24 patients with PI. Patients received either 15 g of oral DKT or placebo daily for 14 days. The effects on upper gastrointestinal motility, frequency of secondary operation and recurrence of PI were investigated. The frequency of surgical operation was significantly lower in patients receiving DKT compared with placebo. Oral administration of DKT was clinically effective for PI in reducing both the need for further surgery and the recurrence of PI.