In order to investigate the effects of different polymer processing methods on the mechanical properties of fiber reinforced thermoplastic polymers, PP/GF composites have been prepared using a pultrusion resin impregnation apparatus developed in our laboratory and compared these with the composites prepared using a twin-screw extruder. The compos ites manufactured by pultrusion resin impregnation apparatus were superior to short fiber reinforced plastics prepared by extrusion with regard to various mechanical properties. The reason for the superiority was ascribed to the reinforcement of resin by long fibers and to high dispersion of the fibers in the matrix. To improve adhesions of fiber surfaces and polymer matrix, maleic anhydride(MA) has been introduced in the PP matrix chain as a compatibilizer. It was found that MA did indeed improve surface adhesion between fibers and polymer matrix and that, as a result, various mechanical properties were markedly enhanced.