Two electrokinetic techniques, electro-osmosis and streaming potential, have been used to investigate the charge characteristics of mixed alumina/titania/silica microfiltration membranes. Both methods can be applied to the membrane itself and streaming potential can be measured during the filtration process, Electroosmosis and streaming potential give very close results in term of isoelectric points, whatever the electrolyte is. The low isoelectric point value suggests that the silica contained in membranes is mainly concentrate at the surface. Both techniques show the modification of the electrokinetic surface properties due to the specific adsorption of sulphate ions onto the membranes surface, The greater zeta potential values determined from electroosmotic flow rate measurements suggest that the shearing plane is nearer the solid surface during electroosmosis. This assumption is strengthened by the increase of the ratio between the zeta potentials determined from both techniques as ionic strength increases.