Mechanical and tribological properties of UHMWPE-based composites with various fillers (aluminum oxyhydroxide micron sized powder, wollastonite microfibers, chopped glass fibers) were studied. The fillers were functionalized with commercially available silane-containing KH550 modifier in order to increase adhesion to the matrix. A comparison on the coupling agent effect on the mechanical and tribological properties of UHMWPE composites loaded at the fillers variation of the content and size is carried out. It is shown that fillers' functionalization is an efficient way to increase wear resistance of UHMWPE composites filled with powders and fibers (increase in wear resistance makes from 1.5 to 3.6 times). On the basis of obtained results, UHMWPE based composites with various size/content studied fillers (powder, fiber) functionalized with the coupling KH550 agent are recommended for industrial application in a wide range of loads and sliding velocities.