Using Y(NO₃)₃·6H₂O as yttrium source, nano-sized Y₂O₃ powder was obtained by calcining the precursor prepared by Pechini method. This Y₂O₃ powder was then used as a sintering additive to fabricate transparent AlON ceramics via pressureless sintering at 1 880 ℃ for 2.5 h. The effects of precursor calcination temperature on the composition, morphology and particle size of Y₂O₃ powder, as well as on the transparency of AlON ceramics were thoroughly studied. The results indicate that increasing calcination temperature of the precursor can promote the decomposition of organic compounds, but it also leads to the growth of Y₂O₃ particles. Residual organic compounds and excessive growth of Y₂O₃ powders are unfavorable for fabrication of AlON ceramics with high transmittance and high relative density. The nano-sized Y₂O₃ powder prepared by calcining the precursor at 900 ℃ for 2 h is favorable for the fabrication of highly transparent AlON ceramics via rapid pressureless sintering. The infrared transmittance of the obtained AlON ceramics reaches up to 83.4% at ~3 750 nm.