We examined the effect of a hot water-soluble extract of Grifola frondosa powder, containing 64% dietary fiber（ YM-11）, on defecation in 37 female volunteers（ age 36.8 ± 7.2 years） with a tendency to be constipated. The subjects were divided into four groups: control group（ placebo diet only） [CG], low-dose group（ YM-11 1.56 g/day） [LG], middle-dose group （YM-11 3.12 g/day）[MG] and high-dose group （YM-11 6.24 g/day） [HG]. The study duration of 6 weeks was divided into 4 periods. First period [I] was pre-test non-intakeperiod [one week]. Second period [II] was placebo diet intake period [two weeks]. Digestible dextrin was given as a placebo diet. All groups were given a placebo diet for two weeks. Third period [III] was a washout, non-intake period [one week]. Fourth period [IV] was test diet intake period [two weeks] for CG, LG, MG and HG. The subjects filled out daily questionnaires concerning their defecation conditions for the entire six weeks. It was found that the number of days with defecation in the MG group was significantly increased during period IV when compared with CG. No deleterious effects were recognized during the studies. These results suggested that YM-11 is a food material with constipation-relieving effects.