A polyblend fiber constituted of polypropylene (PP) and an ethylene-vinyl acetate copolymer modified with mercapto groups was employed for the preparation of an epoxy resin-based composite. This composite presented outstanding impact properties as compared to one prepared with unmodified PP fibers. Scanning electron microscopy indicated the existence of matrix-modified PP fiber adhesion. The results obtained from dynamic mechanical analysis of these composites, such as damping values and the glass transition temperature, taken from the maximum damping temperature, confirm the existence of interfacial adhesion between the matrix and mercapto-modified PP fiber.