The dependence of electrical conductivity of KCl solutions in pores of poly(ethylene terephthalate) and polyimide track-etched membranes (PET TM and PI TM) on the solution concentration and pore diameter has been studied by impedance spectroscopy. It has been found that the conductivity values calculated from the experimental results substantially exceed the standard values in the case of small pore diameters and low concentrations of the solutions, with this difference being more pronounced for PET TM. As the solution concentration and pore diameter increase, the conductivity of the solution in pores tends to the standard value. The revealed effect is explained by the presence of a loose layer on the pore walls that results from the polymer degradation induced by irradiation with high-energy ions. The contact of this layer with the solution gives rise to the gel layer, which is filled with the electrolyte and reduces the measured impedance of the membrane.