Abstract: Crystallization of β nucleated polypropylene was characterized by using the polarized optical microscopy (PLM) and wide－angle X－ray diffraction (XRD) and the research results of the tensile and impact properties indicate that β nucleating agent significantly introduced β－PP crystal and with the increase in β nucleating agent β－PP crystallinity of β nucleated PP increased, so that its impact strength achieved the highest value when there was 0.1% of β nucleating agent in iPP. While the content of β nucleating agent was over 0.1% the impact strength as well as the tensile and fracture strength and Young's modulus of iPP appeared decrease and increase respectively.