The effects of aluminium ions on the crystal structure and magnetic characteristics of the final product and of intermediate phases appearing during the pseudomozphic transformation of the orthorhombic alpha-ferric hydroxide oxide in the tetragonal spinel gamma-ferric oxide were studied by X-ray powder diffraction, infrared spectroscopy and magnetic measurements. Solids solutions of the composition alpha-(Fe1-xAlx)1-y/3(OH)1+yO1-y were formed by incorporation of aluminium from the [Al(OH)4]-solution. The ordering of cationic vacancies and the tetragonal superstructure of gamma-(Fe, Al)2O3 were not affected by the substitution of aluminium for iron.