Aluminum nitride (AlN) polycrystals were prepared by pulse plasma sintering (PPS) technique. The starting AlN powder mixtures were composed with 3.0 wt%, 5.0 wt% and 10 wt% of yttrium oxide (Y₂O₃), respectively. Relative density of each polycrystal was measured by hydrostatic method and evaluated higher than 97%. X-ray diffraction (XRD) method was used for phase examination of the samples after heat treatment. Microstructure examination supported by computer-aided analysis was performed by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results were correlated with thermal conductivity of the samples carried out by laser pulse method (LFA). The influence of the rapid sintering technique and yttrium oxide additive content on the thermal conductivity and microstructure appearance of AlN polycrystals was clearly shown.