Nowadays, there are many studies regarding with nanocomposite production including nano particles which aimed to gain many properties such as better strength, self-cleaning, and resistance to flammability into synthetic polymers. In nanocomposite production, the materials like clay, silica, metal oxides such as TiO2, Al2O3 are used. In present study, three different organically modified montmorillonite (MMT) clays of Cloisite 10A, 15A and 30B (3%) were added into polyethylene terephthalate (PET) polymer. Nanoclay and PET polymer were combined with melt blending method in terms of twin screw extruder. Internal and morphological properties of PET/clay nanocomposites were analyzed with scanning electron microscopy (SEM) images and XRD curves. And also, chemical and thermal properties of nanocomposite samples were studied. The findings and results of nanocomposites were compared with that of PET polymer. At the end of the study, the changes in PET polymer and the effect of clay type on material properties were determined.