Correlation between high-temperature electrical response and microstructural properties of dense hydroxyapatite with average grain size from micrometer to nanometer level in heating/cooling cycle was investigated. Grain interior and grain boundary contributions to overall conductivity were determined. Nanostructured hydroxyapatite exhibited enhanced grain interior conductivity, with significantly higher activation energy (similar to 2.4 eV) than that of coarsed microstructures (similar to 1.7 eV). This difference in activation energies is explained by the possible influence of dehydroxylation during materials fabrication procedure, which affected the amount of OH- ions as the main charge carriers. Grain boundary conductivity was similar for all microstructures, with activation energy above similar to 2 eV, implying the OH- ions migration across grain boundaries. Electrical response in cooling cycle confirmed the trends found during heating. (C) 2014 Elsevier Ltd. All fights reserved.