In this paper, the (In0.5Nb0.5)(x)Ti1-xO2 (with x = 0, 0.005, 0.01, 0.02, 0.05, and 0.1) ceramics were prepared by solid-state reaction. To investigate the humidity sensitive properties, capacitance was measured as a function of relative humidity (RH). Our results reveal that the capacitance increases with the increase in RH and doping level. The best humidity sensitivity of 229.22 pF/%RH was achieved in the sample with x = 10. The humidity sensing mechanism was ascribed to the defects of oxygen vacancies and NbTi ions. Besides, the humidity shows remarkable influence on the dielectric properties of the co-doped samples via the surface-layer effect, which leads to a Maxwell-Wagner relaxation near room temperature. This work underscores that the (In + Nb) co-doped samples are sensitive to the environment moisture. The processing conditions should be optimized for superior dielectric behavior in (In + Nb) co-doped TiO2 ceramics.