LaFeO 3 and Ca x La 1 - x FeO 3 ceramic powders have been prepared by the coprecipitation method from La(NO 3 ) 3 , Fe(NO 3 ) 3 and Ca(NO 3 ) 2 aqueous solutions. The orthorhombic perovskite phases of LaFeO 3 and Ca x La 1 - x FeO 3 , are characterized by X-ray diffraction patterns. The sensors fabricated with those powders have high sensitivity to alcohol. Partial substitution of La 3 + in LaFeO 3 with Ca 2 + can enhance the sensitivity of the materials to reducing gases. The resistance of an LaFeO 3 sensor in air, vacuum and alcohol-containing air has been measured. Complex impedance spectroscopy has been used to try and analyse the gas-sensing mechanism. According to the experimental results, it can be deduced that the surface adsorptive oxygen and lattice oxygen govern the sensing properties of LaFeO 3 and Ca x La 1 - x FeO 3 ceramics.