LaCoO₃ thick-films for gas sensing layers were prepared on alumina substrate by screen printing method. The sensitivities to C₄H_(10), NH₃, NO and CO gases were investigated for different heat treatment temperatures of the films. Their structural properties were examined by X-Ray Diffraction measurements and SEM photographs. The sensitivity of LaCoO₃ thick-film to CO gas was much higher than those of C₄H_(10). NH₃ and NO gases. The optimal heat treatment and operating temperatures were 800 ℃ and 150 ℃, respectively. The sensitivities of LaCoO₃ thick-films to 500ppm and 1250ppm CO gas were 72% and 95%, respectively.