AlN ceramics were prepared via a reaction-bonding technique, using Al and AlN powders as the starting materials. The effects of processing parameters and CaO as an additive were investigated. An AlN ceramic sintered at 1800degreesC with 0.5 wt.% CaO is highly densified and its dielectric constant and dielectric loss tgdelta are 9.4 and 0.002 at 1 MHz, respectively. Its electrical resistivity and Vickers hardness are 2.88 x 10(12) Omega CM, 1210 kg/mm(2), respectively.