Dense β″-alumina electrolyte tubes with thickness less than 50μm were slip cast on a porous substrate of β″-alumina. The resistance of the composite electrolyte was measured by a DC method. The area specific resistance of a thin layer electrolyte versus the full thickness electrolyte was lower by a factor of 1.6. The components of cell resistance were determined. It was concluded that interfacial resistance is a dominant factor in the electrolyte resistance.