Uncompatibilized and compatibilized (polypropylene grafted maleic anhydride as compatibilizer) polyethylene terephthalate (PET)/polypropylene (PP)/TiO2 microfibrillar composites (MFC) were prepared by injection molding of the pelletized PET/PP/TiO2 drawn strands. The morphology of PET fibrils and the distribution of TiO2 particles in the composites were examined. After injection molding the preferential location of TiO2 particles is still preserved. Because of the reinforcement effect of PET fibrils, the tensile properties and impact strength of the PET/PP MFC are improved compared with. the pure PP. Incorporation of TiO2 particles results in decrease of both tensile strength and impact strength of the composites. However, the compatibilized PET/PP/TiO2 MFC demonstrate better mechanical properties compared with the uncompatibilized ones. DMA analysis shows that the glass transition temperature (T-g) of PET in the uncompatibilized PET/PP/TiO2 MFC and the T-g of PP in the compatibilized PET/PP/TiO2 MFC are elevated by about 2 degrees C. The elevation of T-g is attributed to the preferential location of TiO2 particles in the composites. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 3300-3306,2009