A phenyl group was appended to the epoxy-group-containing polymer chain grafted onto the pore surface of a porous hollow-fiber membrane for hydrophobic interaction chromatography. For introduction of the phenyl group at a density sufficient for protein collection, glycidyl methacrylate (GMA) grafted membrane was immersed in 1 M phenol aqueous solution whose pH ranged from 9 to 13. A bovine serum albumin (BSA) buffer solution containing 2 M (NH4)(2)SO4 was forced to permeate through the resultant porous hydrophobic membrane (Ph fiber). The Ph fiber prepared at a lower pH provided a higher elution percentage of BSA when elution was performed with an (NH4)(2)SO4-free buffer. Introduction of the phenyl group at a high density onto the upper part of the shrinking graft layer at a higher pH was demonstrated based on the determination of water breakthrough pressure of the dried Ph fiber, resulting in a lower elution percentage of BSA.