Phase amorphization studies were carried out on mixtures of commercial zirconia and yttria or ceria powders prepared by to high-energy milling. The structural characterization of powders was performed by X-ray diffraction. The specific surface area was determined by nitrogen adsorption, and morphology of powder particles was observed by scanning electron microscopy. For the mixture of zirconia and yttria, the amorphization of yttria is clearly observed for short times of milling, whereas the structure of zirconia remains almost unchanged. The mixture of zirconia and ceria reveals a different degree of amorphization, which occurs simultaneous and gradually with large milling times.