Polyaniline (PANi) nanofiber humidity sensors were prepared by electrospinning (ES) from the N,N-dimethylformamide solution of PANi, poly(vinyl butyral) (PVB) and poly(ethylene oxide) (PEO). Morphologies of the electrospun nanofibers prepared under different ES conditions were observed by scanning electron microscopy. Formation of beads in the nanofibers was found to greatly affect their adhesion to the substrates and the nanostructures. By modulating the composition of ES solution, PANi nanofibers with beads not only showed good adhesion to the electrode and thus good electrical contact, but also maintained relatively high specific surface area. Furthermore, hydrophilicity of the nanofibers was modified by adjusting the ratio of PVB to PEO in the ES solution, which had an effect on their sensing properties. Humidity response of the nanofiber sensors was investigated by measuring their impedance at different humidity levels at room temperature. The nanofiber sensors revealed much higher sensitivity than their film counterparts (impedance changing for three orders of magnitude from 20% to 90%RH). In addition, they were featured with good sensing linearity, fast response (t(90%) of similar to 8 s and 6 s for adsorption and desorption, respectively), small hysteresis (similar to 1%RH) and good repeatability. (C) 2011 Elsevier B.V. All rights reserved.