BaTiO₃ nanofiber has been synthesized by electrospinning and calcination technique. An impedance-type humidity sensor has been fabricated based on this BaTiO₃ nanofiber. It was pleasantly surprised to find that the impedance-type humidity sensor based on BaTiO₃ nanofiber exhibited a fast responserecovery property. The response and recovery time was 4 s and 3 s from 11% to 95% relative humidity, respectively. The complex impedance of the sensor varying more than 4 orders of magnitude in the wide humidity range show excellent sensitivity. These excellent sensing characteristic prove that BaTiO₃ nanofiber can be well applied for humidity sensor. Finally, an ionic conduction model has been proposed to explain the sensing mechanism.