Nanoscale structures of PC/mPP blends with different concentrations have been produced via a simple and versatile method of in situ polymerization of macrocyclic carbonates in the presence of a maleic anhydride polypropylene (mPP). The current method showed that the dispersed phase can be phase separated into a nanostructured morphology of an average diameter as small as 50 nm. The rheological characterization of this system was investigated over a wide range of temperature, shear frequency and, concentration. The viscoelastic behaviors of pure components and blends of concentration less than 40 wt% PC can be well described by the WLF principle. A dramatic decrease in the storage modulus versus temperature at 240°C for blends with composition equal to or higher than 40 wt% PC was observed and may be related to the order-disorder transition of the formation of graft copolymers of PP-g-PC during the in situ polymerization and compatiblization process. The isothermal realtime crystallization kinetics of mPP in the blends with different concentrations was investigated rheologically by monitoring the variation in the elastic modulus, with crystallization time at constant crystallization temperature.