Electrosurface characteristics of polyethyleneterephthalate (PET) track membranes (TMs) with a pore radius of 6.5 to 60 nm used for ultra- and microfiltration have been studied. The results allow for indirect judgments on the track structure and variation in the pore space structure of TMs with the increasing pore radius. Higher values of TM porosity determined from data of the membrane electrical resistance compared with the porosity values obtained from the filtration data suggest that the PET pore surface has a loose structure. The thermal treatment of TMs makes the porosity values determined from the electrical resistance and filtration data closer to one another. The character of changes in the isoelectric point, zeta potential, and surface charge (sigma) indicate that the properties and structure of the PET pore surface depend on the pore radius. The results obtained can be used to predict the separation power of TMs.