The effects of a small dose of mannooligosaccharides (MOS) from coffee mannan on defecating conditions and the human intestinal environment were investigated. Powder of MOS was administered to 13 healthy volunteers in two doses (0.5 g/day and 1.0 g/day) for two weeks. During the MOS 0.5 g/day administration period, defecation frequency was significantly increased from 4.8 times/week to 6.5 times/week (p<0.05), but the ratio of Bifidobacterium to the total anaerobic bacteria did not increase significantly compared with before the administration period. During the MOS 1.0g/day administration period, defecation frequency was significantly increased from 4.8 times/week to 6.3 times/week (p<0.05) and the ratio of fecal Bifidobacterium significantly increased from 14.0% to 25.9% compared with before the period (p<0.05). These results suggest that the minimum effective dose of MOS would range between 0.5 g/day and 1g/day.