The electrical and structural properties of the mixture of Co3O4 and In2O3 were studied. All the samples were added with 2% nanocrystalline SiO2 and sintered at 1000°C for 2 hours. The sintered bodies of the samples were of high density and the average particle size was ~2μm. The materials showed the NTC behavior in a wide temperature range (100-350°C). The resistivity of the materials at room temperature decreased with increase the content of the In2O3 from 0% to 10%. The thermistor constant (B) values and activation energy(E) were 7835, 6637, 5903K, and 0.675, 0.572, and 0.509 eV as the content of In2O3 were 0%, 5% and 10%, respectively.