The effect of coprecipitation reaction course on the magneto-structural properties of iron oxide nanoparticles and, as a consequence, on their heating ability in alternating magnetic fields allowed in magnetic hyperthermia was studied. The parameters of coprecipitation reaction are chosen to ensure the repeatability of nanoparticles features: narrow size distribution, high crystallinity, and magnetic properties. It is established that the reaction should be carried out in an alkaline medium with slow addition of a solution of iron (II) and iron (III) salts to excess alkali. This provides a simultaneous homogeneous nucleation and a rapid growth of nanocrystals during the first minutes of the reaction. After that the reaction proceeds to the stage of slow growth of nanoparticles, which continues up to the complete exhaustion of the solution of salts. Nanoparticles unite in aggregates during the synthesis. The particles in aggregates are characterized by average size of 13 nm and polydispersity index 0.3, mixed phase composition including pure phase magnetite and the products of its oxidation (non-stoichiometric magnetite and maghemite nanoparticles). Material displays magnetization saturation of 56 emu g(-1), non-zero hysteresis and distinct sextets on Mossbauer spectrum at room temperature. A glycerol dispersion of aggregated magnetic nanoparticles provides a temperature increase from 37 degrees C to 45 degrees C within tens of seconds under exposure to alternating magnetic field allowed for application in magnetic hyperthermia. The high heating ability is associated with interparticle magnetic interactions within aggregates leading to the enhancement of energy barrier of magnetization reversal. (C) 2015 Elsevier B.V. All rights reserved.