Oxygen plasma treatments were conducted to improve the adhesive properties of UHMWPE(ultra-high molecular polyethylene) fibers. Oxygen plasma treated fibers were characterized by dynamic contact angle analyzer and XPS(X-ray photoelectron spectroscopy), and interfacial adhesion was measured by fiber pull-out test. The surface of all fibers were analyzed by SEM. Surface free energy increased dramatically by the plasma treatment and polar component was dominant, while dispersive component was negligible. According to the XPS results, increased surface energy was attributed to the oxygen containing groups such as hydroxyl, carbonyl, carboxyl and ester, which could be introduced onto UHMWPE fiber surface by plasma treatment. In general, interfacial shear strength (IFSS) of oxygen plasma treated UHMWPE fibers was much higher than that of untreated fibers. However, comparatively low IFSS values were found at high plasma power, for example at 150w, which could be explained by surface degradation due to strong plasma.