Polycarbophil calcium (Polyful®) is believed to be effective in patients with IBS of both diarrheic and constipated types, because this non-absorbable polymer keeps water content in the stool at the adequate level. Aim of the present study was to study if Polyful could improve diarrhea after ileal J-pouch anal anastomosis (IPAA) for ulcerative colitis. Methods: Twenty-one patients were enrolled in this trial who visited our department as outpatient for the first time after undergoing total proctocolectomy and IPAA in 2- or 3-staged operations. The patients were randomized either into Polyful group (11 patients) or control group (10 patients). Patients were given p.o. bifidobacterium at 3 g/day + Polyful at 3 g/day in Polyful group and bifidobacterium at 3 g/day in control group. Administration of the drugs was continued for consecutive 6 month. We measured anal manometry before and 1 and 6 months after the start of drug-administration, and functional outcome (frequency of defecation per day, stool consistency, and fecal incontinence) was investigated with questionnaire before and 1, 3, and 6 months after the start of drug-administration. Stool consistency was classified into liquid, semi-liquid, semi-solid, or solid. Fecal incontinence was assessed by asking frequency of nocturnal soiling (everyday, 2-3/week, 1/week, 2-3/month, less than 2-3 /month, never). Results: Patients' background did not differ between 2 groups. Two of 11 patients in Polyful group were excluded from the trial, because Polyful made stool consistency too firm and caused difficulty in defecation. Mean maximal resting anal pressure did not differ between Polyful and control groups before administration (52 ± 7 vs. 55 ± 11 cmH2O), 1 month after administration (54 ± 6 vs. 68 ± 9 cmH2O), and 6 months after administration (57 ± 9 vs. 82 ± 14 cmH2O). Frequency of defecation decreased in a postoperative time-dependent manner in Polyful and control groups, but it did not differ between 2 groups. Stool consistency and frequency of nocturnal soiling also improved depending on postoperative time but did not differ between 2 groups.