This work showed that the cold sintering process can resolve high-temperature sintering problems that deteriorate mechanical and functional properties. Potential biomedical materials like alumina-hydroxyapatite nanocomposites can decompose into unwanted phases at high temperatures, which reduces their biomedical properties. In this study, hydroxyapatite reinforced with up to 45 wt% nano-alumina was successfully sintered using cold sintering at a temperature as low as 300 °C. The nanocomposites showed significant hardness (~3 GPa) and full densification without any decomposition or interfacial reactions. Plasma protein adsorption tests revealed the adherence of proteins on the surface of the cold-sintered samples, showing an improved osseointegration behavior in the nano-composites.