The influence of the chronic intake of a newly developed sweetener named "Neosugar" (fructooligosaccharide) on body weight gain, organ weight, serum lipids, fecal excretion and intestinal function was investigated in rats. The following results were obtained. Body weight gain was diminished more severely in rats fed on 20% Neosugar diet than in rats fed on 10% Neosugar diet. The wet weights of cecum and colon were greatly increased by Neosugar feeding. Fecal wet weight was significantly increased and gastrointestinal transit time was shortened by Neosugar feeding compared with those of the control group. Serum triacylglycerol levels were significantly lower in rats fed Neosugar, whereas serum cholesterol levels were similar to those of the control group. Fecal excretions of neutral sterol and volatile fatty acids were significantly increased by Neosugar feeding. These results were quite similar, with the exception of diarrhea to those obtained using a dietary fiber such as glucomannan. Therefore, Neosugar with a pleasant-tasting sweetness appears to be an unavailable oligosaccharide with a dietary-fiber-like action.