The present invention provides a pipecolic acid 4-hydroxylase protein exemplified by the following (A), (B), and (C), having activity to react with L-pipecolic acid in the presence of 2-oxoglutaric acid and iron(II) ions to produce trans-4-hydroxy-L-pipecolic acid, and a method for producing 4-hydroxy amino acid, which method comprises reacting the pipecolic acid 4-hydroxylase protein, cells containing the protein, a treated product of the cells, and/or a culture liquid obtained by culturing the cells, with α-amino acid to produce 4-hydroxy amino acid: (A) a polypeptide comprising the amino acid sequence represented by SEQ ID NO:2, 4, 6, 8, 10, 12, 16, or 18; (B) a polypeptide comprising the amino acid sequence represented by SEQ ID NO:2, 4, 6, 8, 10, 12, 16, or 18 except that one or several amino acids are deleted, substituted, and/or added, and having pipecolic acid 4-hydroxylase activity; and (C) a polypeptide having an amino acid sequence that is not less than 80% identical to the amino acid sequence represented by SEQ ID NO:2, 4, 6, 8, 10, 12, 16, or 18, and having pipecolic acid 4-hydroxylase activity.