Metal oxide semiconductor sensors based on nanocrystalline In2O3 and its composites are found to be very sensitive in detecting low-concentration (5 ppm) gases such as ozone, nitrogen dioxide, formaldehyde and butane. Here, we successfully obtained fiber-shaped In2O3 crystalline nanofibers via electrospun and calcination routes. The gas sensing properties of the In2O3 nanofibers were studied by exposing them to the acetic acid vapor with different concentrations from 500 ppb to 2000 ppm at the optimum operating temperature (250 degrees C). The device possesses ultra-high response of 66.7 toward 2000 ppm acetic acid vapor, low response and recovery times of 25 s and 37 s (100 ppm), respectively, and significant selectivity to acetic acid at 100 ppm. In particular, the sensor based on In2O3 nanofibers has very low detection limit and can reach 500 ppb. Therefore, the presented In2O3 nanofiber sensor can be used in practice in acetic acid detection area in the future.