Germinated barley foodstuff (GBF), which mainly consists of dietary fiber and glutamine-rich protein, is a prebiotic for ulcerative colitis (UC). In our previous study, we carried out a clinical trial of GBF with mildly to moderately active UC patients and showed that GBF treatment was able to attenuate the symptoms of UC in a relatively short-term. The aim of this study was to investigate the efficacy of long-term administration of GBF in the treatment of UC in a multi-center open trial. Twenty-one patients with mildly to moderately active UC received 20-30 g of GBF for 24 weeks in an open-label protocol while baseline treatments (5-amino-salicyrate compounds and/or steroids) were continued. The response to the GBF treatment was evaluated using a clinical scoring and after 24 weeks of observation, the GBF group showed a significant decrease in clinical activity index (especially, the degree of visible blood in stools and the presence of nocturnal diarrhea) compared with the control group (p<0.05). No side effects related to GBF were observed. In conclusion, GBF can reduce the clinical activity of UC over long-term as well as short-term administration. Nutraceutical GBF therapy may have a place in long-term management of UC, but controlled studies are needed to demonstrate its efficacy in the treatment of this disorder.