Polyvinyl alcohol shows a significant impedance response with changing relative humidity (RH) only above 60% RH. Simply fabricated polyvinyl alcohol film as a humidity sensor lacks durability and also shows high impedance. To overcome this problem, polyvinyl alcohol was crosslinked with 4-styrene sulfonate (sodium salt) in the presence of ferrous ions. The best results with the material as a humidity sensor were obtained when polyvinyl alcohol was crosslinked with 4-styrene sulfonate in the presence of ferrous ions at a temperature of 140C for about 1 h and when polyvinyl alcohol, 4- styrene sulfonate (sodium salt hydrate) and FeCl2·4H2O were used in a weight ratio of 10:2:3, respectively. The polymeric mixture of the three materials in water was cast on an alumina substrate (7.5 mm  7.2 mm  0.38 mm in size) prefabricated with interdigitized gold electrodes and was cured at a temperature of 140C for 1 h. The results demonstrate that the logarithm of the impedance decreased linearly with increasing %RH in the range from 30 to 92% RH. Other factors, such as stability, sensitivity and response time for the fabricated sensor, were also determined.