Dense aluminium nitride ceramics were prepared by spark plasma sintering at a lower sintering temperature of 1700uC with Y 2 O 3 , Sm 2 O 3 and Dy 2 O 3 as sintering additives respectively. The effects of three kinds of sintering additives on the phase composition, microstructure and thermal conductivity of AlN ceramics were investigated. The results showed that those sintering additives not only facilitated the densification via the liquid phase sintering mechanism, but also improved thermal conductivity by decreasing oxygen impurity. Sm 2 O 3 could effectively improve thermal conductivity of AlN ceramics compared with Y 2 O 3 and Dy 2 O 3 . Observation by scanning electron microscopy showed that AlN ceramics prepared by spark plasma sintering method manifested quite homogeneous microstructures, but AlN grain sizes and shapes and location of secondary phases varied with the sintering additives. The thermal conductivity of AlN ceramics was mainly affected by the additives through their effects on the growth of AlN grain and the location of secondary phases.