The effects of DC bias on the dielectric and electrical properties of co-doped (In 1/2 Nb 1/2 ) x Ti 1− x O 2 (IN-T), where x = 0.05 and 0.1, and single-doped Ti 0.975 Nb 0.025 O 2 ceramics are investigated. The low-frequency dielectric permittivity ( ′) and loss tangent of IN-T ceramics with x = 0.05 and 0.1 are greatly enhanced by applying a DC bias at 40 and 20 V, respectively, whereas the relatively high-frequency ′ remains unchanged. The induced low-frequency Maxwell-Wagner polarization completely vanishes by immediately applying no DC bias. After overload limited measurement, this polarization permanently emerges without DC bias, whereas the primary polarization remains unchanged. Using combined Z ′′ and M ′′ spectroscopic plots, it is found that the strongly induced-polarizations are contributed from the combination effects of the sample-electrode contact and resistive outer surface. Very high performance of the colossal permittivity in IN-T ceramics is attributed to the formation of a resistive outer-surface layer and insulating grain boundaries. These results not only provide important insights into the origins of the colossal dielectric response in the IN-T ceramic system, but are also important for deciding the doping conditions of TiO 2 -based materials for practical applications. The effects of DC bias on the dielectric and electrical properties of co-doped (In 1/2 Nb 1/2 ) x Ti 1− x O 2 (IN-T), where x = 0.05 and 0.1, and single-doped Ti 0.975 Nb 0.025 O 2 ceramics are investigated.