Aiming to develop a high-performance fiber-reinforced rubber from styrene-butadiene rubber (SBR), we applied a special technique using electron-beam (EB)-irradiation-induced graft polymerization to ultrahigh-molecular-weight-polyethylene (UHMWPE) fibers. The molecular interaction between the grafted UHMWPE fibers and an SBR matrix was studied through the evaluation of the adhesive behavior of the fibers in the SBR matrix. Although UHMWPE was chemically inert, two monomers, styrene and N-vinyl formamide (NVF), were examined for graft polymerization onto the UHMWPE fiber surface. Styrene was not effective, but NVF was graft-polymerized onto the UHMWPE fibers with this special method. A methanol/water mixture and dioxane were used as solvents for NVF, and the effects of the solvents on the grafting percentage of NVF were also examined. The methanol/water mixture was more effective. A grafting percentage of 16.4% was the highest obtained. This improved the adhesive force threefold with respect to that of untreated UHMWPE fibers. These results demonstrated that EB irradiation enabled graft polymerization to occur even on the inert surface of UHMWPE fibers. However, the mechanical properties of the fibers could be compromised according to the dose of EB irradiation. (C) 2004 Wiley Periodicals, Inc.