In this study, nanosize magnetite (Fe3O4) particles have been prepared directly from metallic iron (Fe) powder within distilled water (H2O) by using a planetary ball mill, and the effect of milling time has been investigated. According to Rietveld refinement result obtained from X-ray diffraction (XRD) analyses, the amount of Fe decreases from 98.2% to 0.0%, and it is transformed into Fe3O4, from 1.8% to 100.0%, with the increasing milling time from 1 to 48 h. Due to similar crystal structure of the magnetite and maghemite (gamma-Fe2O3), FTIR and Raman spectroscopies as well as a chemical analysis method was used to verify the magnetite structure. FTIR spectra have clearly revealed absorption peaks around 628, 581 and 443 cm(-1), which are in good agreement with the characteristic absorption peaks of Fe3O4. In addition Raman analysis verified the formation of magnetite phase with a clear main band peak at 671 cm-1. Chemical analyses have shown that the total amount of Fe in the milled sample for 48 h is 73.04%, which contains 24.10% Fe2+ and 49.34% Fe3+. These results are consistent with the theoretically estimated values of the magnetite. It has been observed that the saturation magnetization decreased from 146.02 to 63.68 emu/g with increasing milling time due to the formation of the ferrimagnetic magnetite phase. (C) 2010 Elsevier B.V. All rights reserved.