Nanocomposites of poly(lactic acid), PLA, and poly(lactic acid)/poly(ethylene glycol), PLA/PEG, with clay modified with methyl-bis(2-hydroxyethyl) tallow alkyl ammonium cations (Cloisite 30B) were prepared by melt-blending methods. The influence of PEG content on the structure and thermal properties of nanocomposites was investigated. Comparative samples of the PLA/PEG blends with different PEG content were also considered. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) were used to characterize the studied samples. From XRD, SEM and TEM results, it can be concluded that PEG molecules co-intercalate the silicate layers of Cloisite 30B, together with PLA, allowing better parallel stacking of the silicate layers and the interaction between them. The decrease in the glass transition temperature and crystallization temperature of PLA nanocomposites with an increase in the PEG content, showed the double role of PEG as a plasticizer and as a compatibilizer during the preparation of PLA nanocomposites.