A novel nonreducing sugar comprising glucose as a constituent sugar； a novelenzyme capable of expanding the room for choice of nonreducing sugar andforming the nonreducing sugar； a forming method and production processtherefor； a DNA coding for the enzyme； a recombinant DNA comprising the same；a relevant transformant； and a composition comprising the nonreducing sugarand use thereof. In particular, there is provided anisocyclomaltooligosaccharide having the structure of the general formula:Cyclo{.fwdarw.6)-[.alpha.-D-Glcp-(1.fwdarw.4)]n-.alpha.-D-Glcp-(1.fwdarw.} (1)wherein n is 4 or 5. Further, there are provided a novelisocyclomaltooligosaccharide synthase capable of forming the same； a formingmethod and production process therefor； a DNA coding for the enzyme； arecombinant DNA comprising the same； a relevant transformant； and acomposition comprising the isocyclomaltooligosaccharide or sugar containingthe same and use thereof.
