Polylactic acid (PLA) has inherent drawbacks, such as its amorphous structure, which affect its mechanical and barrier properties. The use of nanofibrillated cellulose (NFC) mixed with PLA for the production of composites has been chosen as a solution to the above problems. A PLA/NFC composite was produced by solution casting. Before use, the cellulose was modified using a silane coupling agent. The composite films were investigated via X-ray diffraction, as well as by mechanical, physical, thermal analyses and by differential scanning calorimeter. The crystallinity was four times that of pure PLA and the water vapor transmission rate decreased by 76.9% with the incorporation of 10 wt% of NFC. The tensile strength of PLA/NFC blend films increased by 98.8% with the incorporation of 5 wt% of NFC. The study demonstrates that the addition of NFC improved the properties of PLA. This provides a solid foundation for the enhancement of the performance of PLA products.