Previous studies reported that by tuning the fusion temperature T (f) (i.e., controlling the melt structure), the beta-nucleation efficiency of beta-nucleated isotactic polypropylene (beta-iPP) can be greatly enhanced, which was called ordered structure effect (OSE). The aim of this study is to investigate the roles of melt structures and molecular weight in non-isothermal crystallization behavior of beta-iPP. Five samples with different molecular weights were prepared, and their melt structures were controlled using differential scanning calorimetry (DSC) by tuning T (f) (T (f) = 200 or 170 A degrees C represent the case of without or with OSE, respectively). Results revealed that for all the samples, the lower the PP molecular weight, the lower the crystallization peak temperature T (c), and the higher the activation energy Delta E, but the occurrence of OSE behavior (i.e., T (f) = 170 A degrees C) can elevate T (c), reduces Delta E and encourages crystallization. The decrease of PP molecular weight decreases beta-phase proportion no matter OSE occurs or not; moreover, for PP with high molecular weight, OSE behavior not only enhances the beta-phase proportion, but also increases the thermal stability of the beta-phase; however, for samples with low molecular weight, OSE behavior enhances the beta-phase proportion in a larger extent, and decreases the thermal stability of the beta-phase. This study provided important understandings in the effect of OSE, cooling rate and PP molecular weight the beta-crystallization of iPP.