Natural hard tissues are composed of a mineral part called hydroxyapatite (HAp), interlocked with collagen fibers. Synthetic composites based hydroxyapatite and polyethylene have been studied for the last three decades. A product with this composition has been commercialized under a trade name (HAPEX™), which is a bio-stable composite. A common problem arouse in these composites, which was the lack of chemical bonding between HAp and each of the polymers. Therefore, improving the overall properties of these composites through chemical modifying the polymeric matrix is the main objective of the current study. An injection molding technique was used to prepare composites based on commercially available hydroxyapatite and both unmodified and chemically-modified versions of UHMWPE. The proportion of HAp added was up to 25% by weight. Results reflected the high sensitivity of the produced samples to slight variations in the assembly of the injection molding as well as changing its parameters. High quality samples with excellent homogeneity were produced. This was also reflected in consistent mechanical behavior during their tensile strength measurements. Morphology of selected composites showed a homogeneous distribution of the HAp particulates in the matrix of the polymers as well as absence of phase separation.