A novel gas sensor composed of electrospun nanofibrous membranes and quartz crystal microbalance (QCM) was successfully fabricated. The electrospun nanofibers with diameter of 100-400 nm can be deposited on the surface of QCM by clectrospinning the homogenous blend solutions of cross-linkable poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA). A series of nanofibrous membranes with various weight percentage of PAA to PVA were fabricated and characterized regarding their morphology and sensitivity to NH3. Sensing experiments were examined by measuring the resonance frequency shifts of QCM which due to the additional mass loading. The results showed that the sensing properties were mainly affected by the content of PAA component in nanofibrous membranes, concentration of NH3, and relative humidity. Additionally, the sensitivity of nanotibrous membranes coated (NMC) QCM sensor was much higher than that of continuous films coated QCM sensor. (C) 2004 Elsevier B.V. All rights reserved.