Quantitative X-ray structural analysis is used for characterizing the atomic-scale structure of γ-FeOOH particles; these particles are formed by immersing pure iron, iron-aluminum, iron-silicon, and iron-phosphorus alloys into an aqueous solution of sodium chloride. The morphology of these γ-FeOOH particles is observed by transmission electron microscopy, and their bonding structure is analyzed using Fourier transform infrared spectroscopy. The realistic atomic-scale structure of the γ-FeOOH particles is estimated by fitting the interference functions with the help of the reverse Monte Carlo simulation technique. The results show that the linkages of fundamental FeO₆ octahedral units in γ-FeOOH had underwent deviation from the ideal crystal structure. The structural deviation and morphological change of the particles were considered to be due to the incorporation of foreign ions during the formation of these particles in the aqueous solution. [DOI: 10.1380/ejssnt.2008.49]