Pure and KCl-doped TiO₂ nanofibers with different crystallographic structures are synthesized by electrospinning and calcination techniques, and their humidity sensing properties are investigated. KCl-doped TiO₂ nanofibers with mixed anatase and rutile structures show the highest sensing performance. The impedance of this sample linearly decreases by more than four orders of magnitude with increasing relative humidity from 11% to 95% on a semilogarithmic scale. Both the response time and recovery time are about 3 s. Excellent selectivity, prominent stability, and good reproducibility are also observed based on this sample. The high humidity sensing performance is explained in terms of the ionic contribution of KCl doping and dissociating promotion of mixed crystallographic structure.