Magnesium with 3 vol% of BN nanoparticles was prepared by milling, compacting and hot extrusion. Pure Mg samples were also compacted and hot extruded under the same conditions. Thermal expansion of cylindrical samples was measured over a wide temperature range from room temperature to 400 degrees C. The temperature dependence of the thermal expansion coefficient of both nanocomposite and extruded Mg differs from the dependence obtained for polycrystalline Mg with the random orientation of grains. The BN nanoparticles decreased the thermal expansion coefficient of magnesium. Pre-deformation of samples influences both the value of the thermal expansion coefficient and the temperature dependence. Changes induced into samples during prestraining are mostly recovered after three temperature runs. Anisotropy in thermal properties of the hexagonal Mg lattice is the reason for the observed anomaly of the temperature dependence of the thermal expansion coefficient. (C) 2016 Elsevier B.V. All rights reserved.