Semiconducting sensors offer an inexpensive and simple method for monitoring gases. Sensors based on the ABO3-type composite oxides materials have an advantage of high stability. The perovskite structures of these compounds are preserved, when an A-site deficiency of some perovskite structure compounds was formed. However, they exhibit particular physical properties. In this paper, La0.9□0.1FeO3 powder with an orthorhombic perovskite phase was prepared by sol-gel method. The electrical properties and CO-sensing characteristics of the La0.9□0.1FeO3 were also investigated. The results demonstrated that the La0.9□0.1FeO3 was a p-type semiconductor material. Compared with LaFeO3, the conductance of La0.9□0.1FeO3 was better than that of LaFeO3. The sensor based on La0.9□0. 1FeO3 showed excellent CO gas-sensing characteristics.