The melting, nonisothermal crystallization behavior and morphology of blends of polypropylene (PP) with random ethylene-propylene copolymer (PP-R) were studied by differential scanning calorimetry, polarized optical microscopy, scanning electron microscopy, and X-ray diffraction. The results showed that PP and PP-R were very miscible and cocrystallizable. Modified Avrami analysis was used to analyze the nonisothermal crystallization kinetics of the blends. The values of the Avrami exponent indicated that the crystallization nucleation of the blends was heterogeneous, the growth of the spherulites was tridimensional, and the crystallization mechanism of PP was not affected by PP-R. The crystallization activation energy was estimated using the Kissinger method. An interesting result was obtained with the modified Avrami analysis and the Kissinger method, whose conclusions were in good agreement. The addition of a minor PP-R phase favored an increase in the overall crystallization rate of PP. Maximum enhancing effect wass found to occur with a PP-R content of 20 wt %. The relationship between the composition and the morphology of the blends is discussed. (c) 2005 Wiley Periodicals, Inc.