The structural properties of precipitates formed by hydrolysis of Fe3+ ions in aqueous solutions, containing NO3- and Cl- ions, were investigated. The reactions of hydrolysis were performed in glass autoclaves at 120-degrees-C. X-ray diffraction showed that alpha-FeOOH and alpha-Fe2O3 were present in hydrolytical products formed in solutions containing NO3- ions, while beta-FeOOH and alpha-Fe2O3 were typical hydrolytical products in solutions containing Cl- ions. In the mixed Fe(NO3)3 + FeCl3 solutions, the phase composition of the hydrolytical products was determined by the concentration of the dominant Fe(III)-salt. Fourier transform infrared spectroscopy and Mossbauer spectroscopy were also used for the structural characterizations of the hydrolytical products. Transmission electron microscopy showed a diversity of shapes of the particles, which depended strongly on the experimental conditions. All types of particle, observed by transmission electron microscopy, were interpreted.