Extensive abnormal grain growth occurs locally at the interface of centrifugally cast bilayers of MgO-doped (1000 ppm) Al2O3 (99.8% purity) during sintering. Results of systematic experiments indicate that the abnormal grain growth is attributable to particle aggregates segregated at the interface during centrifugal casting. Apparently, the particle aggregates contain a higher concentration of impurities than do the fine primary particles, causing local abnormal grain growth at the interface.