Silicone composites reinforced with short eucalyptus pulp fibers were obtained. The composites were prepared with untreated fibers and with fibers modified with a silane coupling agent, vinyltriethoxysilane, with tetrahydrofuran or ethanol as a solvent. The surface treatment improved the adhesion at the fiber-matrix interface, and vinyltriethoxysilane was suitable for forming a covalent and nonhydrolyzed interface in the composites. The thermal stability of the composites was lower than that of the silicone matrix, with a distinct mechanism of degradation, because of the presence of the cellulosic fibers in the composite. The tensile properties of the composites depended more on the fiber dispersion in the matrix than on the nature of the interface. (C) 2003 Wiley Periodicals, Inc.