Uncompatibilized and compatibilized (polypropylene-grafted maleic anhydride (PP-g-MA) as compatibilizer) PET (polyethylene terephthalate)/PP (polypropylene)/TiO2 drawn strands were prepared by extrusion of the blends and cold drawing of the extrudates. In the uncompatibilized drawn strand, the generated PET microfibrils show large aspect ratio and wide distribution in diameter; whereas in the compatibilized drawn strand numbers of short needle-like PET formations appear and demonstrate uniform diameter distribution. Derived from PET droplets, the microfibril morphology is greatly influenced by the size of PET droplets in the extrudates: small droplet deforms into needle-like shape and large one becomes microfibril. In the compatibilized PET/PP/TiO2 extrudate, the size of PET droplet is much smaller than that in the uncompatibilized one. The reduction of droplet size is attributed to the low viscosity ratio between dispersed phase and matrix, which facilitates the break up of the dispersed PET droplets. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 555-562, 2009