The crystallization is the most important structural development in transparent polypropylene(PP). Rapid cooling was applied to make transparent casting and tubular PP films to control the crystallinity and crystalline size. Addition of nucleating agent is another approach to low the crystallinity. In melt casting PP film processing, low molecular PP was often applied to enhance the processing ability but this caused the change of structural development such as orientation and crystallization behaviors in PP films. In this study, we investigated the crystallization behavior of PP with low molecular weight PP and the effect of the nucleating agent on the crystallization was studied as well. It was found that the mixing of low molecular weight PP with PP resulted in the lowering of viscosity and the increase of activation energy in PP. As a result, processing ability and window were enhanced but it caused the increase of crystallinity of PP film. However, our UV spectrum data shows that low molecular weight PP did not affect the transmittance of PP film in the rapid cooling process. It was noticed that the effect nucleating agent on crystallization in PP having low molecular PP is much less than PP. This was understood the comparison of crystallization kinetics between PP with low molecular weight PP and PP with nucleation agent.