Nanomaterials of TiO 2 , (K 0.5 Na 0.5 )NbO 3 , and the TiO 2 / (K 0.5 Na 0.5 )NbO 3 nanocomposite were successfully synthesized by a hydrothermal method. Impedance-type humidity sensors were fabricated based on these materials. Our results reveal that the impedance of the TiO 2 /(K 0.5 Na 0.5 )NbO 3 sensor changes by 5 orders of magnitude with an ultrahigh sensing response of S f = 166 470 recorded at 100 Hz in the tested relative humidity (RH) range of 12− 94%. This value is almost 2 and 4 orders of magnitude larger than that of the (K 0.5 Na 0.5 )NbO 3 and TiO 2 sensors, respectively. Interestingly, satisfactory response/recovery time (25/38 s, within 5 min), very small hysteresis (<5%), excellent stability, and good repeatability were also achieved in the TiO 2 / (K 0.5 Na 0.5 )NbO 3 sensor. The improved sensing properties are ascribed to the synergistic effect of TiO 2 /(K 0.5 Na 0.5 )NbO 3 heterojunction, which contributes the impedance that is susceptible to environmental humidity. This work underscores that it is a facile way to boost humidity-sensing performance by constructing proper nanocomposites.