An isolated gene encodes for a L-proline-3-hydroxylase having the amino acid sequence of SEQ ID NOS: 1, 2, 15, 16 and 17, or for a protein having enzymatic activity to hydroxylate the 3-position of L-proline and to act on free L-proline in the presence of 2-ketoglutaric acid and divalent iron ions to produce cis-3-hydroxy-L-proline. The gene is inserted into a vector and the resulting recombinant DNA is used to create a transformant. L-proline-3-hydroxylase is produced by culturing the transformant in a medium.