The rubber linings used for more than 15 years as a protection of inner walls of steel absorber in flue gas desulfurization system were evaluated by impedance spectroscopy and scanning electron microscopy. The impedance measurements were well reproducible. Evident differences in the impedance spectra were related to different properties of the linings taken from different sites in the absorber. Despite the long time exposure in heavy corrosive environment, the rubber linings kept good dielec. properties and protection efficiency.