Microstructure, phase transformation behavior and dielectric properties of BaTi 1− x (Al 1/2Nb 1/2) x O 3 (0.01≤ x≤0.40) ceramics were investigated. A high level of (Al 1/2Nb 1/2) 4+ substitution for Ti 4+ ions was not conducive to the stability of the perovskite structure and resulted in the formation of BaAl 2O 4. As x was increased, lattice constants and unit cell volume decreased, reached a minimum at x=0.10 and then increased. The BaTi 1− x (Al 1/2Nb 1/2) x O 3 ceramics at room temperature experienced a transformation from ferroelectric to paraelectric phase with increasing (Al 1/2Nb 1/2) 4+ concentration. Meanwhile, permittivity of the BaTi 1− x (Al 1/2Nb 1/2) x O 3 ceramics was markedly reduced, while Q value was slightly increased. Frequency dispersion of dielectric peak was obviously increased as x was increased from 0.01 to 0.10. It is of great interest that a dielectric abnormity represented by a broad dielectric peak at 200–400 K was observed for the composition with x=0.40.