Ternary composites based on isotactic polypropylene (iPP), thermoplastic elastomer, such as ethylene-octhene copolymer (EOC) and poly(ethylene-terephtalate) (PET) textile fibers, have been processed and their properties analyzed. The effect of matrix composition and fiber content on the final properties of the composite has been investigated by means of an experimental design based on a Doehlert Uniform Net. The results have shown that PET fibers act as an effective reinforcing agent, giving rise to a sensible improvement in the tensile and flexural behavior, mainly in matrices with high copolymer percentages. It must be pointed out that the analyzed mechanical properties depend more on the matrix composition than on the fiber percentage. So, as PP content increases, the blend becomes more rigid and stable and a noticeable increase in tensile and flexural modulus and strength, as well as a sensible decrease in tensile elongation are observed. The dynamic-mechanical analysis strongly supports the assumption that the PET fibers behave as a reinforcing agent, showing a sensible increase of the storage modulus in the presence of the fibers. Moreover, this increase is more noticeable as fiber content in the composite is increased. The morphology of the composites has been also analyzed through scanning electron microscopy (SEM).