Abstract: Chromic acid oxidation and sizing agent surface t reatment s were used to modify ult ra high molecularweight polyethylene (U HMWPE) fibers together. The interfacial properties of U HMWPE fiber/ epoxy resin composites were investigated. The result shows that the kinds of resins influence the properties of the composite interface , but the interlaminar shear st rength ( ILSS) of composites is low. Both chromic acid oxidation and sizing agentsurface t reatment s can improve the properties of the composite interface , while the chromic acid oxygen t reatmentweakens the st rength of the fibers if it s t reated time is too long. But the synergy effect s which can improve ILSS ofcomposites obviously without weakening the st rength of the fibers can be achieved by the cooperation of the two different surface t reatment s. This new t reatment is an effective method for surface t reating.