Undoped and Nb-doped TiO2 porous thin films have been obtained through a sol–gel method using analytical grades Ti(OiC3H7)4 and Nb(OC2H5)5 as precursors. The morphology, crystalline microstructure, and the sensing properties towards ethanol and methanol of the obtained thin films have been investigated. The effects of the dopant on the film morphology and on alcohol sensing properties are discussed. Both direct current (DC) and alternating current (AC) measurements were performed at different temperatures in methanol and ethanol ambients to better understand the mechanisms of the alcohol detection. In the presence of a small amount of Nb, the activation energy for electrical conduction decreased. Nb doping improves the selectivity for methanol in the temperature range of 300–400 °C. The Nyquist diagrams showed complex phenomena during alcohol detection.