This paper reports on a study of highly filled composites of polypropylene (PP) and 75 and 85% by weight of oil palm mesocarp fiber (OPF) with and without coupling agent, maleic anhydride-grafted poly (styrene-ethylene/butadiene styrene) (SEBS-MA) and a maleated polypropylene (MAPP). Composites were prepared using a thermokinetic mixer for blending followed by hot pressing. The thermal and mechanical behavior of these composites was investigated by flexural and impact testing and scanning electron microscopy (SEM). Dynamic mechanical analysis (DMA) was also used to study the properties. The MAPP improve the flexural modulus and flexural strength of the composites with 75 and 85wt% of oil palm fiber while SEBS-MA improved the impact strength of the composites. By SEM it was possible to observe some voids, pull out and debonding in the polypropylene, and allowing the observation of level of adhesion between the fiber and matrix. DMTA showed a decrease in storage modulus when high amounts of fiber were added to polypropylene, however, the presence of the SEBS-MA and MAPP increased the storage modulus. This study looks into the effect of MAH modification on the compatibility of OPF and PP, gives a broad overview of an initial study of these new materials.