This article reports the preparation, by means of a masterbatch procedure, of poly (lactic acid) (PLA)/cellulose nanocrystal (CNC) films via premixing 1% wt of CNC into PLA or glycidyl methacrylate (GMA) grafted PLA (g-PLA). These films were obtained by reactive extrusion and subsequent film processing. In this study, 10% wt of GMA with respect to neat PLA was used in the extrusion phase, after that a final grafting degree of 5.69% was obtained. The film obtained by using the masterbatch steps were compared with the system obtained by a direct extrusion of 1% wt of CNC in PLA/g-PLA. Thermogravimetric, crystallization and mechanical properties, as well as morphology of CNC reinforced PLA nanocomposites were characterized. Differential scanning calorimetry and thermogravimetric analysis showed enhanced crystallization ability and an improved heat resistance for the resulting nanocomposites obtained after the use of masterbatches, for example field emission scanning electron microscopy confirmed that the masterbatch preparation procedure was beneficial to the dispersion of CNC in the final nanocomposites. Furthermore, different mechanical performance was obtained when using different masterbatches, which were considered to contribute to extend the applications of PLA based composites as food packaging materials in different sectors.