Abstract Fe 3O 4 particles prepared by oxidation of Fe(OH) 2 precipitated from FeCl 2 solutions containing different amounts of Ni 2+ from 0 to 30 mol% were examined by various means. The thermogravimetry (TG) results show that the addition of Ni 2+ raised the air-oxidation temperature of Fe 3O 4 particles from ca. 200 to ca. 400°C, which means that the Fe 3O 4 particles were stabilized to air-oxidation by the doped Ni 2+. Fe 2+ content of the materials obtained at Ni/(Ni + Fe) ≥ 0.1 mol% was significantly greater than the theoretical Fe 2+ content of Fe 3O 4. Fe 57 Mössbauer spectra indicated that Fe 3+ ions in B sites of the Ni-doped Fe 3O 4 are exchanged in part by Fe 2+. The dc electrical conductivity was increased from 10 −4 to 10 −2 S cm −1 by Ni 2+ loading.