The object of the present invention is to provide an alpha -isomaltosylglucosaccharide-forming enzyme, process of the same, cyclotetrasaccharide, and saccharide composition comprising the saccharide which are obtainable by using the enzyme； and is solved by establishing an alpha -isomaltosylglucosaccharide-forming enzyme which forms a saccharide, having a glucose polymerization degree of at least three and having both the alpha -1,6 glucosidic linkage as a linkage at the non-reducing end and the alpha -1,4 glucosidic linkage other than the linkage at the non-reducing end, by catalyzing the alpha -glucosyl-transfer from a saccharide having a glucose polymerization degree of at least two and having the alpha -1,4 glucosidic linkage as a linkage at the non-reducing end without substantially increasing the reducing power； alpha -isomaltosyl-transferring method using the enzyme； method for forming alpha -isomaltosylglucosaccharide； process for producing a cyclotetrasaccharide having the structure of cycloä->；6)- alpha -D-glucopyranosyl-(1->；3)- alpha -D-glucopyranosyl-(1->；6)- alpha -D-glucopyranosyl-(1->；3)- alpha -D-glucopyranosyl-(1->；ü using both the alpha -isomaltosylglucosaccharide-forming enzyme and the alpha -isomaltosyl-transferring enzyme； and the uses of the saccharides obtainable therewith.L'invention concerne une synthèse d'α-isomaltosylglucosaccharide capable de transférer un α-glucosyl à partir d'un saccharide, portant une liaison α-1,4-glucosyl assurant la liaison au niveau d'une extrémité non-réductrice et possédant un degré de polymérisation du glucose d'au moins 2, sans élever sensiblement la capacité de réduction, en vue de former ainsi un saccharide portant une liaison α-1,6-glucosyl assurant la liaison au niveau de l'extrémité de non-réduction et une liaison α-1,4-glucosyl assurant la liaison au niveau d'une autre extrémité que l'extrémité de non-réduction et possédant un degré de polymérisation du glucose d'au moins 3. L'inventio
