The enzyme-mediated grafting of acrylamide (AM) to ultrahigh molecular weight polyethylene (UHMWPE) fibers using horseradish peroxidase (HRP) was demonstrated. To optimize the reaction condition, the concentrations of monomer, H2O2, the initiator, and time were varied. The grafting results were discussed and a reaction mechanism was proposed. Function groups and structural change of the graft copolymer were determined by FTIR spectroscopic and scanning electron microscopy micrographs for proof of grafting and the results were discussed. Results show that the surface of treated fiber becomes rougher than the untreated surface. Compared to unmodified fiber, modified fiber surface had significantly increased the interfacial shear strength, and carbonyl-stretching regions in the IR spectra. The interfacial shear strength of the UHMWPE fiber increased, clearly indicating that enzymatic-grafted acrylamide could significantly increase the hydrophilicity of the surfaces of UHMWPE fibers. Moreover, the hydrophilicity of treated fiber depends on the monomer concentration, the initiator concentration, and oxidizing agent concentration as well as the time of the reaction. (c) 2005 Wiley Periodicals, Inc.