FT-Raman spectroscopy was used to characterize the thermal conductivity of yttria-doped polycrystalline aluminum nitride (AlN) ceramics. Specimens with different thermal conductivity were prepared using sintering additives of different size, content, and mixing method. The broadening of the Raman mode is caused by point defects and impurities, which affect the thermal conductivity of the AlN grains (lattice thermal conductivity). The width of the Raman line was related to the c-axis lattice parameter contraction, which was caused by aluminum vacancies produced by various defects. A correlation is suggested between the width of the E(2) (high) phonon mode and the lattice thermal conductivity of AlN ceramics.