The effects of partially hydrolyzed guar gum (PHGG) were compared in patients with irritable bowel syndrome, at 10 g/day (N = 40) and 5 g/day (N = 46) for 12 weeks. Gastrointestinal symptoms (GSRS), quality of life (SF-36), and psychological symptoms (HADS) were evaluated at baseline, during treatment (months 1 and 3), and at follow-up (month 6). In both groups symptoms and quality of life improved significantly after the first month of administration until follow-up compared to those at baseline. However, the improvement was significantly reduced at follow-up compared to the end of treatment. PHGG was effective for improving somatic (gastrointestinal symptoms) and psychological (quality of life and psychological distress) symptoms over the short term. Since the improvement tended to decrease after the end of the treatment period, further studies should evaluate the benefits of PHGG at a maintenance dosage.