The phase composition, microstructure, and electrical resistivity of hot-pressed AlN ceramics with 0-4.8 wt% Sm 2 O 3 additive were investigated. The phase composition was approximately consistent with that estimated from the Sm 2 O 3 -Al 2 O 3 phase diagram using the amount of added Sm 2 O 3 and oxygen content of the AlN raw material. When sintered at more than 18001C, the AlN ceramics with 1.0-2.9 wt% Sm 2 O 3 additive contained an Sm-b-alumina phase wetting the grain boundaries, and their electrical resistivity considerably decreased to 10 10 -10 12 X . cm. This resistivity decrease was caused by the continuity of the Smb-alumina phase with a resistivity lower than that of bulk AlN.