In recent years, some Si and Mg containing ceramics have drawn interests in the development of bone implant materials. Forsterite (Mg 2 SiO 4 ), is such materials which introduce recently as a bioceramic. Furthermore, forsterite nanopowder has shown better bio behavior in comparison with micronize forsterite. The objective of present research was to provide and characterize of forsterite nanocrystalline powder by mechanical activation and to evaluate the bio quality. In this study, talc, magnesium carbonate, magnesium oxide, ammonium fluoride and ammonium chloride powders were used as initials materials. Ammonium fluoride and ammonium chloride powders were utilize as the speedup reagent of the process. The influence of different factors such as mechanical activation time, heat treatment temperature and time, using calcined initial materials, ammonium fluoride and ammonium chloride powders on the phase structure and crystallite size of prepared powders was investigated. Various techniques including XRD, STA, XRD, SEM, TEM, DLS, FTIR, EDX, and AAS were employed to evaluate and characterize the produced product. Considering performed experiments and thermodynamic evaluation of the system, some mechanisms was proposed to explain reactions which were done in the procedure of producing nanocrystalline forsterite powder as a hypothesis. Results showed that in the absence of fluorine and chlorine ions, single phase nanocrystalline forsterite powder could be obtained after 5 mechanical activation time of talc and magnesium oxide and subsequent annealing at 1000 ?C for 1 h with crystalline size of about 40 nm. Also, nanocrystalline forsterite powder could be provided by 10 h mechanical activation of talc and magnesium carbonate after post annealing at 1000 ?C for 10 min with crystallite size of 30 nm. Presence of fluorine and chlorine ions caused reduction in mechanical activation time and thermal treatment. In contrast, the crystallite size was increased as a result of changing the forsterite for mechanism. nanocrystalline forsterite powder was obtained after 5 h mechanical activation of talc and magnesium carbonate and adding ammonium fluoride and mixing them for extra 5 min with ball milling and 1 h heat treatment at 1000 ?C with crystalline size of 53 nm. Furthermore, nanocrystalline forsterite powder could be obtained after 5 h mechanical activation of talc and magnesium carbonate and adding ammonium chloride and mixing them for extra 5 min with ball milling and 2 min heat treatment at 1000 ?C. The results of soaking test in SBF showed that forsterite nanopowder unlike micronize forsterite is completely bioactive and could form apatite in SBF, as well. The findings suggest that nanocrystalline forsterite powder possess good bioactivity and might be suitable for medical applications such as filling the bone defects and loading purposes.