Abstract: Influence of the content of PET, properties of matrix, and prosessing temperature on the mechanical and rheological behavior of PP/PET/MFIAA/HET composites was studied. With PET content increased, the number and fine degree of PET micro-fibril increased, which resulted in higher rigidity of the composite but lower toughness. Using PP having a high melt flow rate as the matrix was very beneficial to maintain the microfibril morphology of in situ fiberized composite sample. When using a PP matrix with melt flow rate of 16.2 g/10min, the notched Izod impact strength, tensile yield strength, and flexural modulus of PP/PET/MFIAA/HET with the matrix were 3.49, 0.99, and 1.73 times, respectively, those of neat PP. Effected by both melt-flowability and morphology of the disperse phase, the optimum prosessing temperature for PP/PET/MFIAA/HET should be （200±10）℃. PET microfibril constituted the main reason of the composite melt flow resistance, increasing the content of PET microfibril, the melt-flowability of PP/PET/MFIAA/HET falls rapidly.

Key words: in situ fiberized, polypropylene, poly(ethylene terephthalate), mechanical property, melt flow rate