In this work the feasibility of a high responsive humidity sensor realized through a quartz crystal microbalance functionalized by nanolayers of indium oxide (In2O3) is proposed. The sensing material is deposited by magnetron sputtering method and manufactured in oxygen-free atmosphere, thus named In2O3-x. The humidity-sensing performance of the functionalized quartz sensor was investigated across various humidity levels by monitoring shifts in the quartz resonance frequency induced by absorbed water molecules on the sensing film surface. Appreciable results are observed concerning the humidity sensor response, that follows a linear pattern for humidity levels below approximately 50% RH. At higher RH levels, a notable increase in sensitivity to humidity is observed, likely attributed to the occurrence of water condensation within the pores of the sensing nanomaterial.