Translucent AlN ceramics were fabricated by spark plasma sintering (SPS) with and without CaF2 as sintering additive. An increase in the amount of CaF2 up to 3% in mass did not further increase the density, however improved the IR transmittance. The sample doped with 3% in mass CaF2 yielded the maximum transmittance of 54.7% in medium IR region. The microstructures of the sintered AlN ceramics were investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) attached with an energy dispersive X-ray microanalyzer (EDX). The results showed that the sintered bodies have high relative density and purity. No secondary phase was observed at the grain boundaries or triple grain junctions. Results of the densification process of AlN by SPS were shown.