Crystallization of polypropylene (PP) in unvulcanized blends of PP with the butadiene-styrene block copolymer (SBS) was studied through differential scanning calorimetry (DSC) and X-ray diffraction measurements in the composition range of 0-40 wt % SBS content. Analysis of the crystallization exotherms revealed variation in the crystallization behavior, crystallinity, and crystalline morphology of the PP component in the blends at various levels of SBS concentration. The crystallinity determined by X-ray diffraction and DSC showed identical variations with the blend composition. The tensile and thermal properties of the blends were studied in the entire composition range. Correlations of the tensile properties with the crystallization parameters of the PP component in the blends are also presented.