An object of the present invention is to provide a sugar donating reagent comprising a sugar donor compound other than a sugar nucleotide and an enzyme capable of catalyzing a glycosyl transfer reaction using a sugar donor compound other than a sugar nucleotide. The present invention provides the following: a sugar donating reagent containing a compound of formula (A): wherein R1 is independently selected from hydrogen, or C1-6 alkyl, C2-6 alkenyl, and C2-6 alkynyl in which each of the groups is unsubstituted or substituted with one or more groups selected from OH, F, Cl, Br, I, CN, NO2, and SO2, n is 0, 1, 2, 3, 4 or 5, m is 0 or 1, and X represents a monosaccharide bound via a β bond on its anomeric carbon; a glycosyltransferase capable of catalyzing a glycosyl transfer reaction using the sugar donor; and a glycosyltransferase gene comprising DNA encoding the glycosyltransferase.