Nonwoven and coaxial polypyrrole (PPy)-coated tungsten oxide nanofibers were synthesized via electrospinning and vapor-phase polymerization, and their NH3-sensing characteristics were investigated at various operation temperatures under 100 degrees C. FT-IR and TEM results confirmed the growth of an ultrathin PPy layer on the WO3 surface. The core WO3 nanofiber formed by the axial agglomeration of polycrystalline WO3 nanoparticles had an average diameter of 102 nm, and the thickness of the sheath PPy layer was approximately 5 nm. Upon exposure to 1-20 ppm NH3, the PPy-coated WO3 nanofiber mat exhibited sensitive and fast resistance-increasing (p-type) responses at an operating temperature of 100 degrees C, due to the ultrathin PPy coating and a large surface area of the nanofiber mat. Furthermore, the NH3 detection characteristics revealed strong dependence on operation temperature, which may indicate the involvement of a p-n junction control mechanism in the core-sheath hetero-nanofiber structure. (C) 2013 Elsevier B.V. All rights reserved.