We report an integrated production process that simultaneously nanofibrillates dried pulp and uniformly disperses cellulose nanofibers (CNFs) in resins. Refiner-treated pulp were modified using alkenyl succinic anhydride (ASA) in N-Methyl-2-pyrrolidone (NMP). The ASA treated pulp with DS 0, 0.22, 0.43 and 0.57 was mixed with maleic anhydride-grafted polypropylene (MAPP) powder, CaCO3 and high density polyethylene (HDPE) powder (pulp content: 10 wt%). The mixture was melt-extruded at 140 degrees C with HDPE. The dumbbell-shaped specimens were prepared using injection molding. The SEM images of refiner-treated pulp (DS 0.43) and previously nanofibrillated CNFs (DS 0.44) using a bead mill as a comparison, both of which were extracted from the melt compounded composites, showed comparable degrees of nanofibrillation. The highest mechanical reinforcing efficiency was obtained at DS 0.43, which was shown to exhibit the most fibrillated morphology. The tensile modulus increased from 1.08 GPa for neat HDPE, to 3.46 GPa. The tensile strength also increased from 23 MPa (neat HDPE) to 56 MPa. The mechanical properties were very similar to the bead mill-fibrillated CNF-reinforced composite. This is the first report of nanofibrillation of dried pulp with uniform CNF dispersion into hydrophobic HDPE. We have termed the process the Pulp Direct-Kneading Method.