Perovskite type oxides LaNi 1−x Ti x O 3 (x=0.0–1.0) were prepared by thermal decomposition of amorphous citrate precursors followed by annealing at 700–1000°C in ambient air. These products were characterized by various analytical methods such as XRD, FT-IR, EDAX, SEM and XPS. Ti in the LaNi 1−x Ti x O 3 had significant influence on the crystal size of the nanocrystals and the activation energy (E a ) which was measured at 50–800°C in air atmosphere. The LaNi 1−x Ti x O 3 system showed an interesting metal-insulator transition with increasing Ti concentration, which can be adjusted to enhance the response and selectivity of the materials to acetone. The LaNi 0.5 Ti 0.5 O 3 -based sensor exhibited a quick change in the resistance to 1–5ppm acetone within 40s and took less than 70s for recovery at 350°C, which could hardly be influenced by the environmental humidity. The XPS analysis results showed that the adsorbed oxygen on the surface of sensing material and its concentration are the important factors for the acetone detection. The origin of the gas response is attributed to the thermal reaction, which occurs between acetone and adsorbed oxygen species, forming an acetone–oxygen complex, and then the final product CH 3 COOH is desorbed as a gas at 350°C.