Nanocomposites containing polypropylene (PP), PET, and montmorillonite were prepared in a twin-screw extruder. X-ray diffraction, transmission electron microscopy, scanning electron microscopy, atomic force microscopy, polarized optical microscopy, and differential scanning calorimetry were used to characterize the samples. Intercalated and exfoliated morphology were observed in the nanocomposites. The PET domains usually presented spherical shapes and they were the start point to PP crystallization. The average diameter and number of PET domains was evaluated. The influence of addition of PP-MA as compatibilizer on PP/PET was investigated. The interconnected morphology was observed in the nanocomposite containing PP-MA. The clay located predominantly in the interphase and in the PET phase. The crystallization process was monitored and the PET crystallization rate was slower in the nanocomposites. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 29-36, 2009