This study deals with the structural modifications of a polyamide 6 (PA6) and a miscible blend of this PA6 with an amorphous semi-aromatic copolyamide (PA6/aPA) under tensile drawing. By combining X-ray diffraction and FTIR spectroscopy, the crystalline phase transitions have been investigated as a function of drawing temperature and strain for both systems. A mechanically induced P-a transition has been clearly identified for PA6 at 100 degrees C and above, whereas the PA6/aPA blend undergoes the same evolution at 130 degrees C. These threshold temperatures are very close to the upper limit of the glass-rubber transition of the two systems. This is evidence that the amorphous chain mobility plays a major role on the reorganization capability of the crystalline phase towards its stable form. Further discussion is made regarding the physical origin of this phenomenon. (c) 2007 Elsevier Ltd. All rights reserved.