La0.8Sr0.2Co1-xNixO3-delta films (x = 0.4, 0.5 and 0.6) prepared by dipping method showed maximum sensitivity to 50 ppm CO at a lower operating temperature (180-200 degrees C). The sensing properties of La0.8Sr0.2Co1-xNixO3-delta films to CO are a function of temperature and Ni content. The maximum sensitivity was obtained for a doping of 50 mol% Ni at an operating temperature of 200 degrees C. The response mechanism of sensitivity of metal oxides to CO gas is a surface reaction process and this reaction was thermally activated. The log-log plots of G/G(0) to CO concentration showed a linear relationship. The resistivity of the films is also showed as a function of CO concentration. Tn an exponential plot of resistivity versus CO concentration, the experimental results give a good march to the relationship of R approximate to KCCOalpha.