A novel method of producing high-purity hydroxy-L-pipecolic acids in an efficient and inexpensive manner while suppressing the production of hydroxy-L-proline is provided. The method includes allowing an L-pipecolic acid hydroxylase, a microorganism or cell having the ability to produce the enzyme, a processed product of the microorganism or cell, and/or a culture liquid comprising the enzyme and obtained by culturing the microorganism or cell, to act on L-pipecolic acid as a substrate in the presence of 2-oxoglutaric acid and ferrous ion, wherein the L-pipecolic acid hydroxylase has the properties: (1) the enzyme can act on L-pipecolic acid in the presence of 2-oxoglutaric acid and ferrous ion to add a hydroxy group to the carbon atom at positions 3, 4, and/or 5 of L-pipecolic acid; and (2) the enzyme has a catalytic efficiency (kcat/Km) with L-proline that is equal to or less than 7 times the catalytic efficiency (kcat/Km) with L-pipecolic acid.