Differential diffusion coefficients of beryllium sulfate in water at 298 K and at different concentrations have been measured using a conductimetric cell. The results are discussed on the basis of the Onsager-Fuoss theory. The results were interpreted with success, using the developments introduced by Pikal in the above theory. The cell uses an open-ended capillary method, and a conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries at recorded times.