Humidity sensing composite material is made of nanocrystalline BaTiO3 and polymer polystrene sulfonic sodium (PSS). The composite material is spin-coated onto a ceramics substrate to fabricate humidity sensor. The electrical properties of the sensor are measured. The resistance verse the relative humidity (RH) of the sensor enjoys good sensitivity and linearity in the range of 33-98%RH. The capacitance and the impedance of the sensor change with different frequency and RH. The frequency ranges from 20 Hz to 100 kHz in the plots. Complex impedance plots are semicircles at low RH and a semicircle connected with a line at high RH, respectively. The different kinds of the impedance plots represent the different sensing mechanism for the composite material BaTiO3/PSS humidity sensor. (C) 2002 Elsevier Science B.V. All rights reserved.