PURPOSE: To produce a durable electrolytic electrode substrate by forming a coating layer consisting of a partially oxidized material of nonstoiphiometric composition contg. platinum-group metal, metal such as titanium and oxygen and having specified thickness on the surface of a conductive metallic base material.

CONSTITUTION: The surface of a conductive metallic base material (e.g. titanium and titanium alloy) is roughened to about JIS Ra=10 to 20μm and to about JIS Rmax=50 to 200μm. A coating layer consisting of a partially oxidized material of nonstoichiometric composition contg. platinum-group metal (platinum, rhodium, ruthenium and iridium), at least one kind of metal among titanium, tantalum and niobium and oxygen is formed on the base material surface in 10 to 200μm thickness. As a result, a durable electrode substrate having sufficient resistance to electrolysis resulting from positive and negative inversion is obtained.