Bioactivity of biomaterials is recognized to be of importance and the behavior of nanosized HA and β-TCP particles is described and compared. The study focuses on the influence of the phase transformation and grain size on the reprecipitation of calcium phosphate and the effect of immersion time in SBF on the surface characteristics of the samples. The HA and β-TCP samples were fabricated by mixing the powders in a ball mill, drying, uniaxial pressing and sintering at 1150oC for 240 minute using fixed heating and cooling rates. The densified samples were then immersed in a simulated body fluid (SBF) for controlled periods of time in order to investigate their bioactivities. Changes in the surface structure were examined to investigate and characterize phase formation and the chemical functionality of the samples.