Three different compositions of ZnO-In2O3 composite nanofibers were prepared by electrospinning, and their gas sensing characteristics were compared to those of pure ZnO and In2O3 nanofibers. All ZnO-In2O3 composite nanofibers showed high response to trimethylamine (TMA), relatively low cross-response to C2H5OH, and negligible cross-responses to CO and H-2; pure ZnO or In2O3 nanofibers did not show selective detection of TMA. The maximum responses to 5 ppm TMA of the ZnO-In2O3 composite nanofibers with the compositions of [Zn]:[In] = 67:33, 50:50, and 33:67 by at% were 133.9 at 300 degrees C, 82.9 at 350 degrees C, and 119.4 at 375 degrees C, respectively. Considering all the sensing characteristics such as gas response, selectivity, and sensing/recovering kinetics together, the operation of the ZnO-In2O3 nanofiber sensor with the composition of [Zn]:[In] = 33:67 by at% at 375 degrees C was determined to be in optimal condition to detect TMA. The significant enhancement of gas response and selectivity by the formation of composite nanofibers is discussed in relation to the variation of particle size, the formation of hetero-interfaces between ZnO and In2O3, and the combination of two sensing materials with different catalytic properties, gas adsorption behaviors, and acid-base properties. (C) 2013 Elsevier B.V. All rights reserved.