Ultrafiltration experiments for the optical resolution of racemic phenylalanine were investigated in a DNA solution system and by using immobilized DNA membranes. L-phenylalanine preferentially existed in the permeate solution and D-phenylalanine preferentially existed in the concentrate solution in the ultrafiltration of racemic phenylalanine through the immobilized DNA membranes. This indicates that L-phenylalanine preferentially enters into the pores of the immobilized DNA membranes and permeates through the membranes due to the interaction between DNA and L-phenylalanine. The immobilized DNA membranes were categorized as channel type membranes.