A cellulosic affinity membrane modified with N-acetyl-L-phenylalanine (N-Ac-L-Phe) was prepared intending to separate and purify the serum proteins. A porous cellulose membrane was first reacted with acrylonitrile to afford a cyanoethyl cellulose membrane (CEC membrane). After reduction of the cyano groups of the CEC membrane to obtain aminopropyl cellulose membrane (APC membrane), N-Ac-L-Phe was bound to the APC membrane through amide linkage (APC-Phe membrane). The pH dependence of the adsorption of serum proteins on the APC-Phe membrane was investigated in a dead-end flow mode, using bovine serum albumin (BSA) and gamma-globulin (BgammaG) as model proteins. The adsorption behavior of BSA and BgammaG on the APC-Phe membrane was rather independent of pH, and the amount of BSA adsorbed on the membrane was greater than that of BgammaG. The BSA adsorbed on the APC-Phe membrane was recovered with hydroxycarboxylic acid solutions; whereas, it was not effectively eluted with NaCl solution.