Pure and CuO-loaded In2O3 nanofibers were prepared by electrospinning and their H2S sensing characteristics were investigated. The loading of CuO on In2O3 nanofibers significantly enhanced the gas response (ratio of the resistance in air to that in gas) toward 5ppm H2S from 515 to 1.16×105 at 150°C. The CuO-loaded In2O3 nanofibers also exhibited high gas response (9.17×103 toward 5ppm H2S) at room temperature. The CuO-loaded In2O3 nanofibers showed ultrahigh selectivity to H2S concerning interferences with NO2, H2, CO, NH3, C2H5OH, C3H6O, TMA, C7H8, and C8H10 at room temperature and 150°C. The operation of the sensor using pulse heating was suggested reliable H2S sensing with complete recovery. The ultrasensitivie and ultraselective H2S sensing characteristics are explained in terms of the creation and disruption of p–n junctions in the presence and absence of H2S, respectively, the high specific surface area provided by the networks of one-dimensional polycrystalline nanofibers, and the abundance of p–n junctions due to the uniform mixing between p-CuO and n-In2O3 nanograins within the nanofibers.