In this work, Al₂O₃-ZrO₂ nanocomposites were prepared by spark plasma sintering (SPS) of nanocrystalline and amorphous powders, respectoively, and effects of starting powders on the densification and microstructure of the nanocomposites were investigated. To obtain dense nanocomposites, the minimum SPS temperature for nanocrystal powders was 1 400℃, and the resulting grain sizes were about 320 nm. For amorphous powders, however, the hot pressing temperature was as low as 1 200℃, and the products exhibited finer grains of about 150 nm. It was confirmed that amorphous powders could be hot pressed into dense nanocomposites at lower temperatures than nanocrystalline powders, and the easier densification of amorphous powders was attributed to the phase transformation of amorphous particles in sintering. This finding could provide new guidance for low temperature sintering of bulk nanocomposites.