Crystallization behavior and rheological properties of blends of bisphenol-A polycarbonate (PC) and polypropylene (PP) prepared by screw extrusion have been investigated by differential scanning calorimetry (DSC), polarized-light microscopy, scanning electron microscopy, and a Rheometrics Mechanical Spectrometer. In the study of thermal analysis of PC-PP blends by DSC, double crystallization peaks were observed in the PC-rich compositions. In the study of spherulite of 7/3 PC-PP blend, large droplets (>25 mu m) of PP were crystallized between 115 degrees C and 105 degrees C, and then small droplets (<10 mu m) of PP were crystallized at about 90 degrees C. This result is consistent with the double crystallization behavior such that heterogeneous and homogeneous nucleations have been observed at about 105 degrees C and about 85 degrees C, respectively, by DSC measurements. From the results of rheological properties of the PC-PP blends, the storage modulus of the PC-PP blends at low frequencies has larger value than that of the simple mixing rule. The elasticity increase from the simple mixing rule is consistent with the emulsion model for a dispersed system.