PURPOSE: Inflammatory bowel disease is suggested to result from a dysregulated immune response toward intestinal microflora, which may be restored by probiotic therapy based on the concept of healthy microflora. Ideal probiotic bacteria may be beneficial in inflammatory bowel disease; however, the mechanism of action and the clinical efficacy of probiotic usage are still unclear. In the present study, the effect of exopolysaccharide producing probiotics was evaluated on an experimental colitis model in rats. METHODS: Colitis was induced by intracolonic administration of acetic acid. Then, rats were treated daily with two probiotic strains, Lactobacillus delbrueckii subsp. bulgaricus B3 strain (exopolysaccharide of 211 mg/l: high-EPS group) or Lactobacillus delbrueckii subsp. bulgaricus A13 strain (EPS of 27 mg/l: low-EPS group), which were given into the stomach. The non-colitis-fed control group was only treated with high-exopolysaccharide strain. The model-control and control groups were treated only with tap water. Rats were killed after a seven-day treatment period. Disease activity was quantified by use of histologic scores and colonic myeloperoxidase activity, which is a marker of neutrophil infiltration during inflammation. RESULTS: The enhanced inflammatory response was accompanied by a higher level of myeloperoxidase activity in the colitis group. Histologic scores of colonic damage and myeloperoxidase activity were lower in both probiotic-treated groups compared with those of the colitis control group (P<0.001), although the mentioned scores improved significantly more in the high-EPS group than in the low-EPS group (P<0.001). CONCLUSIONS: Exopolysaccharide-producing probiotics significantly attenuate experimental colitis, which may be mediated by exopolysaccharide in a dose-dependent manner. Therefore, exopolysaccharide-producing probiotics may be a promising therapeutic role in inflammatory bowel disease.