The purpose of the present invention is to provide a novel flavonol 8-hydroxylase. The present invention relates to a flavin enzyme protein having a flavonol 8-hydroxylase activity, and a polynucleotide etc. encoding the same, and so on. The present invention provides: a polynucleotide comprising the nucleotide sequence of SEQ ID NO: 1 or 3 a polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID No. 2 an expression vector and transformant comprising the polynucleotide a method for screening a plant which blooms one or more yellow coloured flowers, by using the polynucleotide a method for producing a plant which blooms one or more yellow coloured flowers by introducing the polynucleotide into host cells and a method for producing a flavin enzyme protein having a flavonol 8-hydroxylase activity, using the transformant.
