Effects of administration of 4^G-β-D-galactosylsucrose (lactosucrose: LS) on fecal microflora, putrefactive products, short-chain fatty acids, weight, moisture and pH, and subjective sensation of defecation were investigated in 13 elderly patients with constipation. The LS mixture used in the present study consisted of LS (59.0%), lactose (22.7%), sucrose (8.4%), fructose (1.6%), glucose (6.8%), and non-identified polysaccharides (0.8%). Subjects were fed 0.32g of LS mixture per kg body weight per day (0.18g of LS per kg body weight per day) for 3 weeks after a one-week control period. The results obtained were as follows: 1. The number and percentage of Bifidobacterium remarkably increased. The frequency of occurrence of Bifidobacterium increased, while that of lecithinase-negative Clostridium decreased. 2. The concentrations of p-cresol, indole, skatole and ammonia in the feces (nmol or μmol/g wet feces) were decreased significantly, and the total fecal excretion of p-cresol and skatole (μmol/week) was also diminished significantly. 3. LS administration caused significant increases in the concentration (μmol/g wet feces) and the total fecal excretion (mmol/week) of acetic and n-butyric acids. 4. Fecal moisture (%) increased significantly, whereas fecal pH decreased. LS also tented to cause a gain in fecal weight (g/week). 5. The stool of patient was softened. The subjective sensation of defecation was improved in 11 out of the 13 patients and unchanged in 2 of them. These results suggest that LS ingestion corrects the fecal condition through improvement of the intestinal microflora.