In present work, Al2O3 nanoceramics toughened with 5 mol% ZrO2 and 10 mol% ZrO2 were prepared by pressureless sintering; polycrystalline ZrO2 powders and Al2O3-ZrO2 amorphous powders were used as dopants in conventional sintering and amorphous-phase-assisted sintering, respectively. In amorphous-phase-assisted sintering, the densification of Al2O3-ZrO2 nanoceramics was highly promoted, and nanoceramics with composition of Al2O3-5 mol% ZrO2 and Al2O3-10 mol% ZrO2 were almost fully densified at temperature as low as 1350 °C. The easy densification was attributed to the metastable state and phase transition of amorphous powders, which acted as sintering aids. The nanoceramics exhibited dense and homogenous mixture of Al2O3 and ZrO2 particles with fine grain size, and the microstructure refinement further contributed to superior mechanical properties with high Vickers hardness, bending strength and Weibull modulus values. This work may provide new guidance for low temperature fabrication of nanoceramics by employing amorphous powders as sintering aids. •The amorphous powders promoted the densification of Al2O3-ZrO2 nanoceramics.•Full dense Al2O3-ZrO2 nanoceramics were obtained by pressureless sintering at 1350 °C.•This work provides new guidance for low temperature fabrication of nanoceramics.