The present invention provides an enzyme which catalyzes a reaction to transfer sugar to a hydroxyl group at position 2' of chalcones and a gene thereof, and preferably an enzyme which catalyzes a reaction to transfer glucose to a hydroxyl group at position 2' of the chalcones. Furthermore, the invention provides a plant whose flower color has been changed using the glycosyltransferase. Using probes corresponding to conservative regions of the glycosyltransferase, some tens of glycosyltransferase genes having nucleotide sequences corresponding to the conservative regions were cloned from flower petal cDNA libraries of carnation and the like. Furthermore, each of the glycosyltransferase genes was expressed in Escherichia coli, activity to transfer glucose to position 2' of the chalcone, i.e., the glycosyltransferase activity at position 2' of chalcone was confirmed in an extract solution of the Escherichia coli, and it was confirmed that cloned genes encoded the glycosyltransferase at position 2'.