The fundamental and practical importance of electrokinetic characterization of porous membranes is now well recognized. However, not enough attention has focused on the fact that the most practically interesting membranes have a multilayer structure. Then, standard electrokinetic methods, such as streaming potential measurement performed through these multilayer membranes, lead to a global signal that does not necessarily reflect the electrokinetic behavior of the skin layer that rules the membrane selectivity. of The relative influence of membrane layers with different physical (pore length, porosity, pore radius) and electrical (zeta potential) properties on tire global streaming potential arising across a two-layer membrane is studied. Each porous layer plays a role in the streaming potential process, but in a wide range of length fraction of support layer the skin layer contributes more than the support layer to the global signal. The contribution of the skin layer increases as its porosity and pore radius decrease, but is little affected by its zeta potential. Nevertheless, in many practical situations, the support layer is likely to play a nonnegligible role on the global signal due to its huge thickness with respect to the skin layer. Therefore, electrokinetic measurements performed with multilayer membranes should be interpreted carefully.