To maintain a large surface area at elevated temperatures, zirconia was added to transition alumina. The addition of a small amount of zirconia resulted in a marked suppression of phase transformation from theta- to alpha-alumina. After heating at 1200(degrees)C, ZrO2-containing alumina exhibited a large surface area of 50 m(2)/g. UV-VIS and XRD measurements indicated that zirconia existed in a high dispersion state after calcining at 800(degrees)C. XPS measurement also showed that zirconia existed as monolayer. Zirconia monolayers are concluded to cover the alumina surface and the interaction between them may be the cause for the suppression of phase transformation and also for the maintenance of the large surface area at elevated temperatures. The interaction remains up to 1200(degrees)C, therefore, theta phase remained at 1200(degrees)C.