The effect of SrO in improving the grain-boundary conduction in gadolinia-doped ceria (GDC) was examined by measuring the spatially resolved local impedance of a SrO-in-diffused GDC specimen containing 500 ppm of SiO2. The addition of SrO increased the grain-boundary conduction by up to similar to 120 times, indicating that SrO effectively mitigates the highly resistive intergranular phase. This paper discusses the possible reasons in terms of the grain-boundary structure, the incorporation of SrO into the GDC lattice, the formation of a second phase, and a scavenging reaction. (c) 2007 The Electrochemical Society.