SnO2 thin films were prepared by the sol-gel process using an alcoholic solution of Sn(OC2H5)(4)2C(2)H(5)OH as the precursor. After subsequent annealing, the temperature of which was varied according to the substrate (oxidised silicon, glass or ceramic glass), the films were characterised by scanning electron microscopy, electron diffraction and Auger electron spectroscopy. The sensitivity of these films to variations in humidity was established for values in the range 0% to 93% relative humidity.