Bio-based PETG (bio-based glycol modified polyethylene terephthalate, Ecozen T95) / clay (organo-modified montmorillonite, OMMT, C10A) nanocomposites were prepared by co-rotating twin screw extruder attached with supercritical carbon dioxide ($scCO_2$) injection system. The effects of nano-clay and $scCO_2$ on the properties of PETG/clay nanocomposites were investigated by measuring thermal, rheological, tensile, impact, and barrier properties. The thermal and mechanical properties decreased with increasing nano-clay content, but they recovered or even exceeded the properties of neat PETG as $scCO_2$ was added. It was verified due to a good dispersion of the nano-clay in PETG matrix for PETG/clay nanocomposites by XRD, SEM, and TEM. It was thought that $scCO_2$ could be an effective exfoliation agent for many nanocomposites systems as well as for bio-based PET/clay nanocomposites.