A simple nondestructive method is presented to characterize the physical properties of ultrafiltration membranes. The technique utilizes voltammetry at the interface between two immiscible electrolyte solutions (ITIES) and has been applied to commercially available γ-alumina membranes. Upon the application of a potential difference across the ITIES, the voltammetric response resulting from an ion transfer is a direct measure of the membrane porosity. The technique has been applied to the measurement of the fractional porous area (porosity) and the membrane thickness. The reported technique offers advantages over existing methods such as being easy to use, reproducible, inexpensive, and nondestructive. Furthermore, unlike many optical techniques, this method is not limited by a minimum nominal pore size and has thus been used to make measurements when the reported nominal pore diameter is as small as 20 nm.