The present invention relates to a polypeptide having a &Dgr;5 fatty acid desaturation activity and a polynucleotide encoding the polypeptide as well as use thereof. For example, the present invention relates to a polypeptide, comprising (a) the amino acid sequence represented by SEQ ID NO: 2; or (b) the amino acid sequence in which one or more amino acids are substituted, deleted, inserted or added in the amino acid sequence represented by SEQ ID NO: 2, and having the &Dgr;5 fatty acid desaturation activity; an antibody capable of binding to this polypeptide; a polynucleotide encoding the polypeptide; a vector comprising this polynucleotide; a cell or transformant introduced with the polynucleotide; a method of producing a fatty acid using the cell, and so on.
