Zirconia was prepared by firing the coprecipitate from ZrOCl2 and AlCl3 mixed aqueous solution with ammonia. When fired above 600degreesC, the products were fine crystalline tetragonal zirconia of crystallite size <10 nm. In previous studies, the tetragonal phase had been assumed to be a (Zr1-x4+Alx3+)O2-x/2 solid solution, where x less than or equal to 0.25. However, X-ray diffraction pattern simulation and Al K-edge XANES spectroscopy confirmed the present product to be a mixture of t-ZrO2 fine powder with a small amount of delta-Al2O3 of very low crystallinity, even below the expected compositional range of x less than or equal to 0.25 in the (Zr1-x4+Alx3+)O2-x/2 solid solution.