The main topics from the results of the studies by the author and collaboraters during the four decades are reviewed. The studies are related to glucanotransfer activity of amylases and related enzymescyclodextrin glucanotransferase, α-amylase, D-enzyme and branching enzyme-and included the following subjects. 1) Coupling sugar (maltooligosyl sucrose) was produced from the mixture of dextrin and sucrose by Cyclodextrin glucanotransferase. The cariogenicity of the coupling sugar was studied by a group at the Japanese National Institute of Health and several universities, and coupling sugar was proved to be an anticariogenic sweetener. It was the first example of a so-called functional oligosaccharide which had a physiological property in addition to the conventional function of sweeteners. 2) Synthesis of some glucosides: hesperdin dihydrochalcone glucoside, glucosyl stebioside, glucosyl hesperidin and hydroquinone glucoside. Among them, stevioside is about 140 fold as sweet as sucrose, but has a slightly bitter taste and after taste. The taste was improved by enzymic glucosidation. Hydroquinone glucoside inhibited tyrosinase activity, and consequently the melanin accumulation of human skin. Applications for hydroquinoe glucoside in the cosmetic field have started recently. 3) Discovery of cycloamylose containing 17 or more glucose residues. Potato D-enzyme catalyzes an intramolecular transglycosylation reaction on amylose to produce cycloamylose, a novel α-1, 4 glucan composed of 17 or more glucose residues. X-ray structure of a cycloamylose with 26 glucose residues was explained. 4) Development of cyclic clusterdextrin, a new dextrin containing cyclic parts. Branching enzymes catalyze the cyclization of amylose and amylopectin. The product from amylopectin had a narrow molecular weight distribution compared with those of commercial dextrins. The cyclic clusterdextrin was soluble in water to give a highly stable and clear solution. The solution had a low propensity for retrogradation.