Cellulose nanofibrils were prepared from starting material microcrystalline cellulose (MCC) by an application of a high-pressure homogenizer at 20,000 psi and treatment consisting of 0, 1, 2, 5, 10, 15 and 20 passes. Hydroxypropyl cellulose (HPC) films reinforced with those cellulose nanofibrils were prepared at different filler loading levels. According to the morphology study by scanning electron microscope (SEM), the complete filbrillation of the bulk cellulose fibrils to nanoscale and high aspect ratio was accomplished by the homogenization process. The HPC film reinforced with cellulose fibrils after the 5.10 passes through the homogenizer improved significantly the tensile modulus and strength values for the HPC films. The thermal stability of HPC films is not affected by the addition of the cellulose nanofibrils, although MCC has the lower thermal stability than neat HPC. The development of novel cellulose nanofibrils and composites with high strength can be achieved by an application of the homogenization process.