The influence of the nature of the process control agent (PCA) used in the mechanosynthesis of the magnetite nanoparticles has been studied. The two-step route used here for obtaining nanocrystalline/nanoparticles Fe3O4 consists of a heat treatment, to prepare well-crystallised magnetite, followed by the mechanosynthesis process. Dry milled magnetite samples have been obtained as a reference, using the same conditions (duration and energy), to determine the influence of the process control agents (PCA). Three different PCAs have been used: benzene, ethanol and oleic acid. The characterisation of the magnetite particles has been performed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), magnetic measurements M(H), differential scanning calorimetry (DSC) and thermogravimetric (TG) measurements and Scanning Electron Microscopy (SEM). XRD and SEM analysis revealed a different processing mechanism for the two milling modes, wet and dry. In the case of dry milling, even for short milling times, iron contamination and formation of a wustite - FeO phase is noticed. The use of the PCA during the milling process limits the above-mentioned contamination. Ethanol and benzene uses as PCA lead to synthesis of fine uniform sized particles. SEM images reveal the presence on nanoparticles. In the case of oleic acid, DSC, TG and magnetic measurements revealed the presence of a thin layer of oleic acid adsorbed on the particles. FTIR analysis highlighted the presence of both free and bonded oleic acid. The magnetisation of the samples was found to be linked to the powder contamination (FeO or oleic acid), structural defects or finite size effects. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.