This work presents the preparation of blended (HDPE/UHMWPE) nanocomposites with graphite nanosheets (GNS) by melt mixing (differing compositions) in an internal mixer. After graphite flake treatments to obtain GNS; HDPE/UHMWPE blends are produced using a Haake internal mixer with further compression molding. The blends were prepared as mixes of 0, 10, 20, and 30 wt% of UHMWPE in HDPE. The blend with the best mechanical and thermal properties is chosen to prepare the nanocomposites. The nanocomposites are produced from the 10 wt% UHMWPE in HDPE blend, with 0.5 and 1.0 wt% GNS using the same method as used for obtaining the blends. The functionalized graphite FTIR spectrum revealed functionalization with silane. However, after the ultrasonic bath these groups left the graphitic structure, and as shown by the diffractogram (XRD) and SEM images, good exfoliation continued. The nanocomposite blend with 10 wt% UHMWPE presented higher tensile strength values than pure UHMWPE, and the nanocomposite blend with the lower GNS percentage (0.5 wt%) presented the highest tensile strength. However the nanocomposite with 1.0 wt% GNS presented an increase in crystallization temperature.