Charged dielectrics can cause an electrostatic discharge (ESD) that damages electronic circuits because of the electromagnetic noise associated with the discharge. Newly developed anti-ESD polymers are expected to be 'anti-ESD polymer insulating materials', but the mechanism of their action against ESD has not been explained. Since the anti-ESD polymers contain some kind of polymer solid electrolyte, they should be able to be characterized by the behavior of their internal space charge. By measuring the space charge distribution of an anti-ESD polymer using the pulsed electroacoustic method under de electric field, we found that the polymer was effective in preventing ESD because the internal space charge near the surface partially compensates the electric field of the external charge on the surface. We also found indications that the internal space charge behavior is related to the dispersion of the polymer solid electrolyte.