We report the synthesis of CuO-SnO2 nanocomposite nanofibers of various chemical compositions via electrospinning as well as their excellent H2S sensing capabilities. The results of X-ray diffraction and high-resolution electron transmission microscopy demonstrate that the nanofibers are a mixture of the tetragonal rutile structure of SnO2 and the monoclinic structure of CuO in the form of nanograins. Each nanograin shows a single phase of either CuO or SnO2, instead of forming their solid-solution phase. In other words, a CuO-SnO2 nanocomposite structure is realized in a true sense. The sensing properties of the CuO-SnO2 nanocomposite nanofibers are well explained based on the creation and extinction of the p-n junctions between CuO and SnO2 nanograins. The p-n junctions that are readily created in such nanocomposite due to the presence of nanograins as well as the high specific surface area provided by the one-dimensional nanofiber shape are responsible for the outstanding H2S sensing performances of the CuO-SnO2 nanofibers. (C) 2012 Elsevier B.V. All rights reserved.