Short date palm tree lignocellulosic fibers have been used as a reinforcing phase in commodity thermoplastic matrices [poly(propylene) and low density polyethylene]. Compatibilization of the fibers was carried out with the use of maleic anhydride copolymers. The morphology, thermal and mechanical properties of the resulting composites were characterized using SEM, DSC and tensile tests. The reinforcing capability of the unmodified fibers was found to depend on the nature of the matrix and the main parameter governing the composite behavior was the degree of crystallinity of the matrix. Compatibilization was reported to enhance the mechanical performances for both sets of composites up to a critical amount of compatibilizer beyond which the degree of crystallinity of the matrix decreases.