The crystal structures of different grades of cast polypropylene (CPP) extrudates were characterized by Differential Scanning Calorimetry (DSC) and Wide Angle X-ray Diffraction (WAXD). The effects of the crystallization temperature, draw ratio, and cooling rate on crystal structure are discussed in detail. The results demonstrate that stretching cannot induce the formation of the gamma crystal, but the crystallization temperature and the cooling rate do affect the formation of the gamma crystal. The slower the cooling rate, the more easily they crystal develops. It was found that at the optimum crystallization temperature (T-c) of about 110 degreesC, the gamma crystal developed distinctly, and a slower cooling rate made the formation of gamma crystal easier. Also, the crystal structures of different resins at the same conditions were discriminative, suggesting that the formation of the gamma crystal was due to interruptions of comonomer units in the isotactic propylene sequences, which prevented the PP chain segment from entering the crystal lattice of the alpha crystal in some degree. If the length of the comonomer sequences was shorter and the distribution of the comonomer units more symmetrical, the formation of the gamma crystal would be more distinct. (C) 2004 society of Plastics Engineers.