Abstract: The surface of ultrahigh molecular weight polyethylene (UHMWPE) fibers was grafted by an acrylamide. Using a horseradish peroxidase (HRP) as catalyst in hydrogen peroxide, the reaction was generated by free radical, which is formed by oxidizing o-methoxyphenol. The best condition of graft polymerization was determined by the orthogonal test. The results of the fiber pull out test show that after enzymatic treatment, the interfacial shear strength of the system surface increased, and the pull out strength of treated UHMWPE fibers increased by 69.8%. Its optimum value appears when the initiator concentration, H₂O₂ concentration and the reaction time are 0.5%, 0.03%, and 90 min, respectively. Infrared spectroscopy (IR) and Scanning Electron Microscopy (SEM) show that roughness of UHMWPE surface increased, and a new radical appears in IR. The probable catalytic mechanism of HRP was discussed.