Herbaceous peony (Paeonia lactiflora Pall.) is an excellent material for studying the formation of flower colour because of its abundant colour. The full-length cDNA of a UDP-glucose: Flavonoid 5-O-glucosyltransferase gene (UF5GT) containing 1629 bp nucleotides was obtained from P. lactiflora. The expression patterns of nine related anthocyanin biosynthetic genes (PlPSY, PlCHS, PlCHI, PlF3H, PlF3'H, PlDFR, PlANS, PlUF3GT and PlUF5GT) in diurnal variation petals showed that their expression peaks were basically at 15:00 and the expression patterns were consistent with the trend of sampling conditions except individual gene. And the highest expression levels were in PlCHS, PlDFR and PlUF3GT, which could be the candidates to regulate P. lactiflora flower colour by means of genetic engineering.