Polyacrylonitrile ultrafiltration membranes have been widely used in many separation processes. In this paper, horseradish peroxidase was immobilized onto polyacrylonitrile ultrafiltration membrane by crosslinking with glutaraldehyde. The immobilized enzyme possessed a protein loading of 0.025mg/cm(membrane)(2) and a specific activity of 105U/mg(protein) (105mol/min/mg(protein)). The initial modified and immobilized membranes were observed using SEM and FTIR. Potential applications of HRP membranes were investigated in the removal of phenol through oxidation with the addition of hydrogen peroxide. The optimum pH of the immobilized enzyme was determined to be 6.0, and the optimum hydrogen peroxide concentration to be 30mmol/L. Almost 100% removal of phenol (1 approximate to 10mg/L) from water was achieved by HRP membranes. For high concentrated solutions, successive cycles were successfully used to improve the degree of phenol oxidation. Furthermore, the immobilized horseradish peroxidase was operationally stable. These results suggest that the HRP membrane has promising applications for the removal of phenol.