In this paper the effect of different organosepiolites on PET matrix was evaluated through the analyses of Melt Flow Index (MFI) and Intrinsic Viscosity (IV) of the nanocomposites. PET/sepiolite nanocomposites were produced through a two-stage process. The masterbatch production was done in a melt compounding extruder, and then these were taken to an injection machine, where different specimens were obtained for characterization purposes. Two types of organomodifiers were tested, silanes in one hand and a quaternary ammonium salt on the other. Thermal analyses were done to determine thermal stability of the organomodifiers. Then, different experiments were carried out increasing the concentration of coupling agents to analyse its effect on PET matrix degradation. As results indicate a high degree of degradation of the nanocomposites matrix, pyromellitic dianhydride (PMDA) was added as chain extender to react with PET molecular chains, with the aim of increasing its molecular weight (Mw).