The crystalline structure, morphology, and nonisothermal crystallization behavior of isotactic polypropylene (iPP) with and without a novel rare earth-containing beta-nucleating agent (WBG) were investigated with wide-angle X-ray diffraction, polar optical microscopy, and differential scanning calorimetry. WBG Could induce the formation of the form, and a higher proportion of the beta form could be obtained by the combined effect of the optimum WBG concentration and a lower cooling rate. The content of the form Could reach more than 0.90 in a 0.08 wt % WBG nucleated sample at cooling rates lower than 5 degrees C/min. Polar optical microscopy showed that WBG led to substantial changes in both the morphological development and crystallization process of iPP. At all the studied cooling rates, the temperature at which the maximum rate of crystallization occurred was increased by 8-11 degrees C in the presence of the nucleating agent. An analysis of the nonisothermal crystallization kinetics also revealed that the introduction of WBG significantly shortened both the apparent incubation period for crystallization and the overall crystallization time. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 1076-1085, 2009