A partially hydrolyzed guar gum preparation (PHGG, average molecular weight: 20, 000), obtained as a water-soluble dietary fiber by digestion of guar gum with β-D-endomannanase, was ad-ministered as a beverage (11g a day, bid) to 15 constipated women for 3 weeks. Defecating frequency, pH, weight, moisture, and bacterial flora of the feces were investigated and compared with the control periods. Average total dietary fiber taken from food was 9.7±0.1g/day during the experiment. PHGG caused an increase in the defecating frequency from 0.46±0.05 (frequency/day, M±SE) to 0.63±0.05. Fecal moisture signif-icantly increased from 69.1% in the control period to 73.8% by ingestion of PHGG. Fecal moisture content also increased consistent with lowering the pH of feces (γ=-0.478). The frequency of Lactobacillus spp. occurrence in feces significantly increased (p<0.05) compared with the control period. These results clearly indicate that PHGG softens and improves the output of feces.