The present invention relates to a process for producing a fatty acid, which includes feeding a liquid mixture formed of two liquid phases that flow in a co-current manner into a fixed bed-type reaction column packed with immobilized lipase, and performing a hydrolysis reaction when the two liquid phases are in contact with the immobilized lipase in the fixed-bed reaction column; wherein the fixed-bed reaction column comprises partition plates so as to comprise a plurality of tube- shaped structures, wherein each tube-shaped structure has a cross -section which is rectangular, circular, oval, or polygonal in shape with at least a part being unclosed and the cross-section has a representative length of 100 mm or less.