The effects of indigestible dextrin on serum lipid and glucose concentrations, large intestinal functions, feces states, and gastrointestinal transit time were studied with 90 male Sprague-Dawley rats. Diets contained 0.5% cellulose(0.5CL control), 10% cellulose(10CL), and 10% indigestible dextrin I (10ID-I), respectively and were fed to the rats for 3 weeks. Serum cholesterol and LDL-cholesterol concentrations were lower in rats fed the 10ID-I diet. Serum triglyceride concentration was lower in rats fed the 10CL diet. Cecal content and cecum weight significantly increased in the rats fed the 10ID- I diet. Cecal pH of the rats fed the 10ID-I diet was lower than that of the rats fed the 0.5CL diet. Changes of fecal output were not observed in case of 0.5CL and 10ID-I diets but a significant increase was observed in the case of 10CL. Gastrointestinal transit time of 10ID-I was the longest among the three diets. These results demonstrate that indigestible dextrin delivered to the cecum was not digested and increased the cecal mass. Indigestible dextrin improves colonic health of rats by inducing low pH of the cecum. (Korean J Nutrition 31(6) 991-998, 1998)