Studying the isotropisation kinetics during melting of a drawn poly(ethylene terephthalate) (PET)/polyamide 12 (PA12) blend (60/40 wt %) at T-m(PA12) < T-a < T-m(PET) by means of wide-angle X-ray scattering (WAXS) from synchrotron radiation a transcrystallization behaviour of PA12 was observed. It was also found that the nonisothermal transcrystallization behaviour of PA12 taking place during cooling down of the molten PA12 is characterized by reorientation of PA12 chain axis by 90 degrees with respect of PET chains axis and of the starting chains axis direction as concluded from the WAXS patterns. A conclusion is drawn that PET microfibrils are not only effective nuclei for transcrystallization of the matrix but they cause a drastic reorientation of the matrix chains placing them perpendicular to the initial common for both PET and PA12 orientation direction.