: The objective of this study was the synthesis of glass ionomer–forsterite nanocomposite and the survey of the effect of addition of forsterite nanoparticles to the ceramic part of glass ionomer cement (GIC) in order to improvement its mechanical properties and bioactivity. So, forsterite nanoparticles were made by the sol-gel process. X-ray diffraction (XRD) technique was used in order to phase structure characterization and determination of grain size of produced forsterite nanopowder. Glass ionomer–forsterite nanocomposite was fabricated via adding 1, 2, 3 and 4 wt.% of forsterite nanoparticles to the ceramic part of commercial GIC (Fuji II GC). In order to study of mechanical properties of produced nanocomposite, the compressive strength (CS), three-point flexural strength (FS) and diametral tensile strength (DTS) of specimens were measured. Statistical analysis was done using one way ANOVA and differences were considered significant if P 0.05. The morphology of fracture surface of specimens was examined using scanning electron microscopy (SEM) technique. Fluoride ion release experiment and simulated body fluid (SBF) were used in order to study of the fluoride ion release from produced nanocomposite and its in vitro bioactivity, respectively. The results of XRD analysis confirmed that nanocrystalline and pure forsterite powder was obtained. On base of mechanical properties measurements, the optimum weight percentage of forsterite nanoparticles for enhancement of CS, FS, and DTS were gotten equal to 3, 1 and 1 wt.%, respectively. Fluoride ion release evaluation showed that the values of released fluoride ions from produced nanocomposite are somewhat less than Fuji II GC during test time. SEM images, the pH changes of the SBF and results of the inductively coupled plasma Optical Emission Spectroscopy (ICP-OES), Fourier transform infra-red spectroscopy (FTIR) and Energy dispersive X-ray spectroscopy (EDS) confirmed the bioactivity of the produced nanocomposite, too. Statistical analysis showed that the differences between the results of all groups were significant (P 0.05). The results showed that glass ionomer-forsterite nanocomposite containing 1wt.% forsterite nanoparticles could be a good candidate in high-stress dental restorations and orthopedic implants, through of improvement of mechanical properties and bioactivity and preservation of fluoride ion release behavior. Key words: Glass ionomer cement, Forsterite nanoparticles, Sol-gel, Mechanical properties, Fluoride ion release, Bioactivity.