Polyaniline (PANI) intercalated MoO3 thin films with b-axis preferred orientation were obtained by an ex-situ intercalation process. A MoO3 thin film was first deposited on LaAlO3(100) substrate at 500 degrees C by chemical vapour deposition. It was then partly reduced to [Na (H2O)(2)](x)MoO3 after which intercalation of polyaniline into MoO3 by ion-exchange reaction was performed to obtain (PANI)(x)MoO3. The resulting (PANI)(x)MoO3 thin film exhibits an increase in electrical resistivity in response to volatile organic compounds. Good sensitivity and selectivity of (PANI)(x)MoO3 thin film to formaldehyde and acetaldehyde vapours was observed. (c) 2006 Elsevier B.V. All rights reserved.