Background: Hydroxyapatite (Ca10(PO4)6(OH)2) is the major inorganic component of hard tissues, the best bio-active materials, which is compatible with the bone tissue. In addition, hydroxyapatite nanoparticles (Nano-HA) have received enormous national attention in medical and dental applications recently; but the ultimate fate of the Nano-HA within the body is still unknown. Degradation products of nanomaterials are potentially cytotoxic. Thus, it is essential to assess biocompatibility before their usage in clinical applications.Aim: Purpose of this research is to evaluate toxicity of hydroxyapatite nano particles on the human peripheral blood mononuclear cells.Methods: In this experimental study, nano sized, rod-like hydroxyapatite particles sterilizalied then HPBMCs were cultured on 96-well plate. Cells were exposed to Nano-HA at the following concentrations: 15.5, 32, 65, 125, 250, 500, 1000, 2000, 4000, 8000 ppm. Later, For measuring the cell vitality, MTT method was utilized. Measuring the photo absorption was done by ELISA READER system at 570 nm, which evaluated the vitality of cell by the value of MTT absorption cells. The statistical ANOVA test was used in this study Results: All of drug concentration were effective in Loweriy eellular biologic ectivity but none of them were statistically significant.Conclusion: Therefore as a conclusion we can adjudicate that “Nano-HA” biomaterial is the material which is compatibility with the human blood mononuclear cells.