An electrode for superoxide anions which contains a conductive component and, superimposed on a surface thereof, a film resulting from electrolytic polymerization of a metal thiofurylporphyrin/axial ligand complex; and a sensor for measuring a superoxide anion concentration including the same. The electrode for superoxide anions can prevent poisoning by a catalyst poison such as hydrogen peroxide. Accordingly, in any of in vitro or in vivo environments, this electrode for superoxide anions enables detection of superoxide anion radicals without suffering any influence from a catalyst poison such as hydrogen peroxide. Moreover, quantitative assay of superoxide anions can be performed with this electrode for superoxide anion in combination with a counter electrode or a reference electrode. Thus, this electrode for superoxide anions can find wide applicability in various fields.