In many applications, e.g., wire and cable insulation, hot water pipe, high-temperature properties of polymer are essential. This article presents the use of silane crosslinking together with the addition of particular filter in improving the thermal and mechanical properties of ethylene-octene copolymer (EOC). The effects of filler surface characteristics on siloxane network structure developed and final properties of the crosslinked products are discussed. The results show an increase in the decomposition temperature of EOC more than 50 degrees C after modification. Only crosslinked composites are able to withstand the high-temperature environment of aging test which is beyond the melting temperature of the matrix polymer. The crosslinked composites filled with calcium carbonate show superior properties to those with silica, due to a higher crosslink density and tighter network structure formed. The silane coupling mechanism and the presence of bound polymer on silica surfaces cause difficulties for the crosslink formation in the silica filled systems. However, an advantageous influence of both silane coupling and crosslink reaction in the silica filled composites is seen on the enhanced tensile strength and modulus of the materials. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 424-430, 2010