In this study, nanocomposites based on of β-tri calcium phosphate (β-TCP) and 2.5-10 wt% merwinite nanoparticles were prepared and sintered at 1100-1300°c. The mechanical properties were investigated by measuring compressive strength and fracture toughness. Structural properties were evaluated by XRD, TEM and SEM analysis, and the in vitro bioactivity was studied by soaking the samples in simulated body fluid (SBF). The mechanical strength of the sintered samples were increased, by increasing the amount of merwinite phase up to 5 wt%, whereas it decreased when the samples were sintered at 1100 and 1200°c. Nanostructured calcium phosphate layer was formed on the surfaces of the nanocomposites within 1 day immersion in simulated body fluid. Because of appropriate mechanical properties the composite is suggested to be used as substitute for hard tissue.