PURPOSE: Some patients who underwent low anterior resection of the rectum do not show satisfying improvement in their anorectal function despite of long-term conservative management. The aim of this prospective study was to evaluate whether loperamide or diazepam could improve anorectal symptoms. METHODS: Fifty-two patients who continued to complain of problems with their anorectal function at least 6 months (mean: 1 year and 2 months) after the operation were recruited. The patients were randomly divided into two groups, and 2 mg of loperamide (loperamide-group, n=24) or diazepam (diazepam-group, n=28) was given orally three times a day for 4 weeks. Standardized interviews concerning anorectal function and anorectal physiologic studies were performed before medication, at the fourth week of medication, and 4 weeks after withdrawal from the medication. RESULTS: In both groups during the medication, daily stool frequency, the number of patients with urgency to defecate, and incontinence score significantly decreased, and maximal resting pressure and urge sensation volume significantly increased. In the diazepam-group, the decrease in daily stool frequency, the number of patients with urgency to defecate, and the increase in urge sensation volume continued after withdrawal from the medication. CONCLUSION: Loperamide or diazepam could improve the long-lasting fecal incontinence symptoms after low anterior resection in patients with rectal cancer. In the process, the increase in maximal resting pressure and urge sensation volume seemed to contribute to a significant degree.