The contamination of water by sulphate is a pollution problem that has increased in severity in recent decades. The behaviour of cellulose acetate membranes in the treatment by reverse osmosis of aqueous sulphate solutions is described. Experimental essays were performed in a commercial cross flow test module in which solutions of sulphate of con-centrations between 0.145 kg/m(3) and 25.455 kg/m(3) were treated. Recycling of both the concentrate and permeate was carried out in order to keep the concentration constant and to simulate a continuous process in a quasi-stationary state. A simulation model described for a semi-batch and unsteady-state system was applied to our experimental conditions (batch and steady-state mode) and verified. The model uses the solution diffusion approach to depict the mass transfer through the membrane, while the constants are determined experimentally. Good agreement between the experimental and model results was obtained, so that the model can be considered suitable for simulating of reverse osmosis treatment of aqueous sulphate solutions by cellulose acetate membranes in the concentrations range studied.