Abstract: Using polypropylene (PP) and poly ( ethylene terephthalate) (PET) with the multifunction interlayer active agent riveting-embedded (PET-MFIAA)，the PET-MFIAA/PP in situ fiberized composites were prepared by blending-extrusion-drawing. By means of scanning electronic microscope (SEM)，polarized microscope (PLM) and mechanical properties measuring，the PET microfibril morphology，fracture surface morphology of samples and the mechanical properties of the PET-MFIAA/PP were studied and contrasted with two other kinds of in situ fiberized composites of PET/PP and MFIAA/PET/PP. The results show that there is strong interfacial adhesion in the PET-MFIAA/PP in situ fiberized composites，which has structure characteristics of powerful interaction between PET microfibril and PP matrix，PET microfibril presenting profiled morphology of diameter variation and concave and convex surface，flexible interlayer，etc. Both rigidity and toughness of PET-MFIAA/PP are apparently higher than those of the pure PP. The tensile yield strength，flexural modulus and notched izod impact strength of the PET-MFIAA/PP composite containing 7. 00 % MFIAA are raised to 1.04 times，1.23 times and 1.79 times as the pure PP respectively.