The scavenging of a resistive siliceous phase via the addition of Al2O3 was studied, using imaging secondary-ion mass spectroscopy (SIMS), given the improved grain-boundary conductivity in 8-mol%-yttria-stabilized zirconia (8YSZ). The grain-boundary resistivity in 8YSZ decreased noticeably with the addition of 1 mol% of Al2O3. Strong SiO2 segregation at the grain boundaries was observed in a SIMS map of pure 8YSZ that contained 120 ppm of SiO2 (by weight). The addition of 1 mol% of Al2O3 caused the SiO2 to gather around the Al2O3 particles. The present observations provided direct and visual evidence of SiO2 segregation at the gain boundaries (which had a deleterious effect on grain-boundary conductivity) and the scavenging of SiO2 via Al2O3 addition.