Microfibrillated cellulose (MFC) in polymer has attracted increasing applications with the fully bioderived nanocomposites. Polymer composites from polylactide (PLA) and MFC were prepared using two different fiber preparations. Freezedried MFC was prepared and directly mixed with PLA in an internal mixer. The MFC premixed with PLA in an organic solvent was prepared, followed by an internal mixer for another composite. In addition, grafting cellulose on PLA using a compatibilizer was performed. In this research, composites containing 10 wt% MFC were used to investigate the influence of processing and compatibilizer on the mechanical and thermal properties. The processing procedure had a great influence on the mechanical and physical properties. The tensile strength was increased with filler loading and showed different values depending on the premixing step prior to processing. The storage modulus and loss tangent confirmed that the compatibilizer acted as the role of a bridge between filler and matrix, enhancing the mechanical properties. This experiment was conducted to compare the effect of pretreatment on the change of mechanical and thermal properties by using freeze-dried cellulose and cellulose suspension substituted with an organic solvent.