Microcrystalline cellulose (MCC) and polyamide 6 (PA6) fibers are used for the manufacture of thermoplastic nanocomposites. From the MCC (0.5 wt% of water), the cellulose nanofiber (CNF) with a mean fiber diameter below 30 nm is successfully obtained by a high pressure homogenizer with different processing conditions, such as various number of pass, nozzle size and operation pressure. As the operation pass number and pressure are increased, the specific surface area (SSA) of CNFs is increased due to the fibrillation during the homogenization process. The large surface area of CNF can improve the reinforcement effects for their nanocomposites. The composite papers, consisting of CNFs and PA6 fibers, are fabricated by a wet-laid sheet forming process. In this step, the pre-hydrolyzed silane coupling agent (0.1, 0.5, and 1.0 wt% in water) is added into the CNF slurry. The CNF/PA6 composites are pressed by a high pressure (3.4 and 4.8 MPa) calendering system. The tensile strengths of nanocomposites are increased by more than two times (max. 16.4 MPa) compared to PA6 100% sheets (6 MPa) due to the silane treatment, calendering process and reinforcement of CNFs.