Diffusion coefficients of the Fe-2(SO4)(3))/water system at T = 298.15 K and at concentrations between 0.050 mol.dm (3) and 0.200 mol.dm (3) have been measured, using a conductimetric cell and an automatic apparatus to follow diffusion. The cell uses an open-ended capillary method. A conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries at recorded times. These data are discussed on the basis of the Onsager-Fuoss model. The diffusion of Fe-2(SO4)(3) is clearly affected by the Fe (III) hydrolysis. These data permit us to have a better understanding of the structure of such systems and the thermodynamic behaviour of ferric sulphate in different media. (C) 2012 Elsevier Ltd. All rights reserved.