This paper reports that nano- La0.7Pb0.3FeO3 powders can be used as a new type of gas-sensing material for detecting CO. The La0.7Pb0.3FeO3 powders were prepared by a citric method. The powders are characterized by X-ray diffraction, showing that the La0.7Pb0.3FeO3 is still perovskite phase with orthorhombic structure and its crystallite size is about 17 nm, smaller than that of LaFeO3. The La0.7Pb0.3FeO3 is a kind of p-type semiconductive material, and its conductivity is higher than that of LaFeO3. The CO sensitivity of La0.7Pb0.3FeO3-based sensor is investigated. We found that La3+ partly substituted by Pb2+ in LaFeO3 can enhance its sensitivity for CO gas.