4^G-Galactosylsucrose (β-D-fructofuranosyl 4-ο -β-D-galactopyranosyl-α-D-glucopyranoside or lactosucrose; LS) is selectively utilized by bifidobacteria in the human intestinal canal. This saccharide is found in the fermentation of yogurt containing sucrose as a sweetener. In 1957, Avigad and co-workers reported that LS was synthesized from sucrose and lactose by transfructosylation of levan sucrase. Production of LS was then proposed, using transfructosylation of levan sucrase or transgalactosylation of β-galactosidase from sucrose and lactose. However, industrial production of LS was not undertaken at that time. We have therefore attempted to establish production of LS, and to develop utilization of LS as an ingredient in health foods. Arthrobacter sp. K-1 isolated from soil produces β-fructofuranosidase. The enzyme catalyzes both transfructosylation and hydrolysis when incubated with only sucrose. However, in the presence of a suitable acceptor such as lactose, the enzyme predominantly catalyzes transfructosylation and transfers the fructosyl residue preferentially to an acceptor molecule rather than to a sucrose molecule. LS is commercially produced as follows. The mixture of sucrose and lactose (45-55: 55-45, w/w) is solubilized in water at 40% (w/w), and incubated with Arthrobacter sp. β-fructofuranosidase and invertase-deficient yeast at a temperature of 30-35°C for 24 h. The yeast is added to remove residual products of glucose derived from sucrose by assimilation, as these materials inhibit LS production. Utilizing this method, LS production is increased more than 65%. After heating is used to terminate the reaction, the reaction mixture is purified by decoloration, carbonation, filtration, desalination, ultra filtration and concentration. LS syrup containing over 55% LS can then be obtained. Three kinds of products, Nyuka-oligo LS-40 L, LS-55 L, and LS-55 P are commercially available, with LS contents of 40, 55, and 55%, respectively. The sweetness of LS, LS-40 L, LS-55 L, and LS-55 P is about 30%, 79%, 50-55% that of sucrose, respectively. These products have a high quality taste similar to sucrose. LS is not digestible in the human small intestine, but human intestinal microorganisms, particularly bifidobacteria, ferment it. The minimum effective dose of LS to improve intestinal microflora fecal conditions and defecation is 2 g/day. The saccharide is less likely to result in watery stool compared to other low-caloric sweetening agents. LS is used in soda, soft drinks, frozen yogurt, candy, biscuits, cookies, powdered soft drinks, sweet pastries (e.g., croissants), and table