Broom fibers have been used as reinforcement for the conventional polypropylene (iPP) and a maleate modified one (iPPMA). A conventional alkaline treatment and a steam explosion extraction process were applied to obtain the cellulosic material from broom branches. Composites were prepared by melt mixing materials with different weight percentages of broom fibers. Also ternary blends (iPPMA/iPP/broom fibers 5/45/50 wt) were obtained to examine the possibility of utilizing the maleate polypropylene as a compatibilizing agent. The fibers and the composites were thermally, morphologically, and mechanically characterized. Water absorption tests, to examine the behavior of these materials in wet conditions, were also performed. Particular attention was addressed to the study of the fiber/matrix interfacial adhesion. The results showed that the iPPMA-based composites, reinforced with alkaline extracted broom fibers, present specific mechanical properties competitive with those of the homologous polypropylene-based materials reinforced with short glass fibers. The ternary blends gave similar properties to those of the corresponding whole iPPMA-based composites. It is considered that the esteric linkage between the cellulose {OH, and the maleic anhydride groups grafted on the polypropylene backbone is greatly responsible for the similarity in the properties. In spite of better adhesion observed in the samples reinforced by the steam-exploded fibers, less improvement of the mechanical properties was observed, owing to significant damage of the structure of the fibers during the steam explosion process. A general decrease of mechanical properties is observed in normal polypropylene-based composites. The results are also supported by the water absorption tests: whereby the iPPMA-based composites showed good capability to return their dry properties when kept in an oven after wetting for many days.