In the last years research and development of new materials and methods for bone repairing and substitution has been a priority in the biomedicine field. HDPE/Hydroxyapatite (HA) composites have been previously used successfully for such purposes. In this study, HDPE/HA composites prepared in an internal mixer were characterized. Mixing conditions, such as temperature and mixing rate, were optimized. Results showed that high mixing rates and lower temperatures improved the filler dispersion in the polymeric matrix. At optimal conditions composites with 10, 20, 30 pph of HA were prepared and their rheological, mechanical, thermal and thermodegradative properties were determined to establish the optimum filler content. Inclusion of HA particles decreased the melt flow index. The incorporation of HA also increased the Young's Modulus and strength at break and decreased the elongation at break due to elasticity loss. Thermal properties and initial degradation temperature were not affected with the inclusion of the filler but an enhancement in the activation energy was observed. A titanate coupling agent (Lica 12) was added to composites to improve the interfacial interactions. Lica 12 did not produce any variation in the mechanical and rheological behavior of composites. A slight decrease in composite crystallinity was detected for composites coupled with 0.5, 0.7 and 1.0% Lica 12. The thermal stability increased with the addition of the coupling agent.