The object of the present invention is to provide a polypeptide which can be used to produce a saccharide having a structure of cyclo{.fwdarw.6)-.alpha.-D-glucopyranosyl-(1.fwdarw.3)-.alpha.-D-glucopyr- anosyl-(1.fwdarw.6)-.alpha.-D-glucopyranosyl-(1.fwdarw.3)-.alpha.-D-glucop- yranosyl-(1.fwdarw.}, a DNA encoding the polypeptide, and uses thereof. The present invention solves the above object by establishing a polypeptide which has an enzymatic activity to produce a saccharide having a structure of cyclo{.fwdarw.6}-.alpha.-D-glucopyranosyl-(1.fwdarw.3)-.alpha.-D-glucopyr- anosyl-(1.fwdarw.6)-.alpha.-D-glucopyranosyl-(1.fwdarw.3)-.alpha.-D-glucop- yranosyl-(1.fwdarw.} from a saccharide with a glucose polymerization degree of 3 or higher and bearing 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.-isomaltosyl-transfer, and having an amino acid sequence of either SEQ ID NO:1 or SEQ ID NO:2, or that which is a member selected from the group consisting of amino acid sequences having deletion, replacement, or addition of one or more amino acid residues therein or thereto, a DNA encoding the polypeptide, and uses thereof.