hort fiber thermoplastic composites are under attention due to their recyclability and ease of production. Having superior properties to the other polyolefins, polypropylene has great amount of applicatio and it is very desirable in the composite industry. PET fiber is a good option as the reinforcement because of having good mechanical properties and high toughness. Adding a compoatibilizer can strengthen fiber-matrix interactions and, therefore, improve the mechanical properties. In this study, pre-pegs of PP and PET fibers were prepared in both presence and absence of GMA and MA as compatibilizers in an internal mixer at 180 ?C and 60RPM and then, they were molded by hot press. It was confirmed that tensile and flexural modulus were enhanced by adding PET fibers and the flexural modulus of GMA compatibilized samples with 15 weight percent fiber load was increased 45 percent. The HDT results show an increase of 15 ?C for GMA containing samples and none-compatibilized ones. It was observed that adding fiber has good influence on enhancing the impact strength and by adding 15wt% of fiber, the impact strength showed 40% enhancement. This increase was greater for unmodified samples for existing of more wasting energy mechanisms while fracture verified by SEM, but at higher fiber loads like 20 wt%, the impact resistance of the modified samples were anticipated. The SEM micrographs showd that in the presence of compatibilizers, interfacial adhesion is stronger compare to that for none-compatibilized ones. In ordet to study transcrystalline(TC) layer optical microscopy was applied and it was confirmed that only non-compatibilized samples show a little amount of TC around the fibers. In this research, two parameters of Gc and Kc were determined considering LEFM assumptions and also some micromechanical models were used to evaluate the composite Young modulus and among them, Halpin-Tsai and Pan equations had better predictions. Key words: Thermoplastic composite, Glycidyl Methacrylate, Polypropylene, PET fiber, Maleic Anhydride, Short fiber composite
