The electrical properties of (Li, Al)-doped NiO ceramics (i.e., Li0.05Al0.04Ni0.91O, Li0.05Al0.06Ni0.89O, and Li0.05Al0.10Ni0.85O) synthesized by a simple thermal decomposition route were investigated. It was observed that the grain size of the ceramics was affected by the Al content. Impedance analysis confirmed that these ceramics had an electrically heterogeneous structure that was responsible for the giant dielectric response. Interestingly, the Al-dopant had not only the strong effects on the electrical transport character at grain boundaries, but also on the conductivity in the grain interiors. (C) 2009 Elsevier B.V. All rights reserved.