Ab stract Although hydroxyapatite nanopowder is very excellent for bone tralantation, the low fracture toughness has limited its use in orthopedics affairs specially under loading implants, therefore in composite form it uses more extensive. In comparison to other bioceramics such as bioactive glass, glass ceramic and hydroxyapatite, forsterite has higher mechanical properties. So we should expect hydroxyapatite-forsterite composite be useful in order to improve mechanichal and bioactive properties. The purpose of this study was fabrication and characterization of hydroxyapatite-forsterite composite nanopowder prepared by sol-gel method and nano-structured bulk by two step sintering process. In this research hydroxyapatite-forsterite composite nanopowder was produced via the sol-gel process. Then in order to create a compact and dense structure of composite hydroxyapatite-forsterite with nano-structured characteristics the two-step sintering method was occurred. The experiment was designed by Taguchi method and the secondary sintering temperature, primary and secondary sintering time were optimized with the help of Qualitek software. The effect of sintering temperature and time on bulk density, grain size, phase structure and mechanical properties were investigated. The x-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) techniques were used to characterize hydroxyapatite-forsterite composite nanopowder and dense nano-structured bulk of sintered nano-powder production. In order to evaluate the bioactivity properties of dense nano-structured bulk of sintered hydroxyapatite-forsterite composite fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used. The scanning electron microscope (SEM) was used in order to assess the morphology of cells cultured on the surface of nano-structured bulk sintered. The results showed that particle size of hydroxyapatite-forsterite composite nanopowder was about 30 nm. Grain size of dense nano-structured bulk via a two-step sintering method was about 20 to 50 nm. The highest bulk density was obtained in the initial temperature of 1200°C, secondary temperature 1100°C, initial sintering time 5min and a second sintering time 25h. During immersion of nano-structured bulk sintered of hydroxyapatite-forsterite composite nanopowder in simulated body fluid, apatite layer was formed, so it can be concluded that it had a good bioactivity. Cell culture test results indicated the effect of nontoxicity of hydroxyapatite-forsterite composite nanopowder on the cells. Cell adhesion test results cells growth and attached to themselves and spread on the surface of nanostructured bulk sintered. Bulk density of sintered by two-step sintering method under optimal conditions, was 94% of theoretical density. Fracture toughness of dense nanostructured bulk sintered of hydroxyapatite-forsterite composite nano powder was higher than fracture toughness of hydroxyapatite. Keywords : Nanocomposite, Hydroxyapatite-Forsterite, Sol-gel, Two step sintering, nano-structured bulk