Formation of beta-cylindrites of isotactic polypropylene under various wall shear stress (sigma(w)), supercooled temperature of melt (T-e) and crystallization temperature (T-c) has been investigated by polarized light microscopy (PLM), wide angle X-ray diffraction (WAXD), and differential scanning calorimeter (DSC). To have better control over the thermomechanical history, instead of a reciprocating screw, the samples were prepared by extruding supercooled melt through capillary die. beta-cylindrites can be observed by PLM in the extruded specimen even at a lower sigma(w) (0.020 MPa), and the number of beta-cylindrites nuclei increases rapidly with the lowering of Te. The nucleation density of beta-cylindrites increases with the raising of wall shear stress under a given Te of 160 degrees C. Furthermore, at lower supercooled temperature of melt (145 degrees C), the radius of beta-cylindrites decreases with the increasing of sigma(w), and the number of beta-cylindrites nuclei almost remain invariant. At relatively higher sigma(w) (0.090 MPa), a saturation of beta-cylindrites nuclei is observed with decreasing T. A modified model based on above results has been proposed to explain the effect of the original structure of quiescent supercooled melt on the formation of beta-cylindrites under low shear stress. (C) 2011 Elsevier Ltd. All rights reserved.