Abstract: An improved valve metal electrolytic capacitor is disclosed, such as an aluminum electrolytic capacitor, as well as a method of making same wherein the improvement comprises forming a hydration resistant composite layer on the valve metal, including a valve metal oxide dielectric layer, by anodizing the valve metal in an aqueous phosphorus-containing organic electrolyte selected from the class consisting of phosphonic acid, phosphinic acid and mixtures of the same dissolved in an aqueous liquid to provide an electrolytic capacitor with increased resistance to hydration.