Long fiber reinforced thermoplastic composites are one of the fastest growing segments experiencing 30 % growth per year, over the last decade. This study describes the development of long fiber reinforced thermoplastic (LFRT) composites and the effect of fiber length on mold and process parameters of injection molding process. LFRT pellets of different sizes were prepared by an extrusion process using a specially designed impregnation the and palletized into different lengths. These pellets were injection molded to develop LFRT composites. Fiber length distributions were analyzed using a profile projector and an image analyzer software system. Maleic anhydride grafted polypropylene (MA-g-PP) was added to improve the adhesion between glass fibers and polypropylene. Improvement in mechanical properties were analyzed for different pellet sizes with different fiber content for long fiber reinforced polypropylene (LFPP) and long fiber reinforced polyamide (LFPA) composite.