The low-resistivity material (LRM) is widely used to decrease the power-frequency grounding resistances of grounding devices for transmission lines in the regions with high soil resistivity. The study about the influence of the LRM on impulse performances of grounding devices cannot be found in literature. Experimental results of lightning impulse properties of grounding devices covered with LRM were presented in this paper. The influences of impulse current, geometrical dimensions of grounding devices, and soil resistivity on impulse grounding resistance and impulse coefficient of grounding devices with the LRM coverings are still the same with those without the LRM coverings. The impulse grounding resistance decreases from about 25% to 45% when the LRM covering is used. The fitting formulae to calculate the reducing ratio of impulse grounding resistance of different grounding devices are provided. On the other hand, the influence of LRM on the effective impulse length of grounding electrodes is discussed.