Composites based on maleated polypropylene and methyl cellulosic fiber were prepared by extrusion followed by injection molding. The methyl cellulosic fiber was pretreated with tetrabutyl orthotitanate prior to compounding. The mechanical and thermal properties, as well as morphology of composites, were investigated by means of tensile, impact, dynamic mechanical analysis, thermogravimetric measurements, and scanning electron microscopy. Static tensile tests showed that the stiffness and tensile strength of composites tend to increase with increasing fiber content. However, the elongation at break appeared to decrease with increasing fiber content. In contrast, the impact strength of composites increased slightly with increasing fiber content. The improvements in tensile and impact properties were attributed to the interaction between the functional group of maleic anhydride and tetrabutyl orthotitanate. Such interaction tended to improve the interfacial bonding between the methyl cellulosic fiber and polypropylene matrix. Thermogravimetric measurements revealed that the incorporation of methyl cellulosic fiber into maleated polypropylene results in a marked reduction of thermo-oxidative stability. The effects of coupling agent additions on the mechanical properties of composites are discussed.