In order to evaluate the available energy of dietary fiber materials, the fermentability was estimated from breath hydrogen excretion for 8 h after ingestion of 5g of dietary fiber materials in healthy human subjects. Fructo-oligosaccharide, of which available energy has been 2kcal/g, was used as a positive control, because it is not digested and is completely fermented by intestinal microbes. The following results were obtained based on the variable fermentability of each dietary fiber material. 1) Polydextrose, indigestible dextrin, partially hydrolyzed guar gum, lowered molecular alginate-Na and glucomannanwere estimated as 1 kcal/g. 2) Nondigestible starch, which was resistant for the fermentation by intestinal microbes, was estimated as Okcal/g. 3) Cellulose, which is a water-insoluble dietary fiber, was slowly fermented and was estimated as l kcal/g.These results demonstrate that the method using breath hydrogen analysis is available to estimate the fermentability of dietary fiber in human gastrointestinal tract. However, it was not enough to collect expiratory gas of every 30 min period for 8 h after ingestion of dietary fiber materials. The fermentation of each dietary fiber material did not have been finished yet till 8 h after ingestion. Therefore, if the breath is collected for longer periods, the fermentability might increase and the available energy would be changed from the values as mention above. Another study with longer periods of breath collection will be needed.