This paper investigates the ability of boron (B) as a dopant in TiO2 nanofibers for use in humidity sensing. B-doped TiO2 nanofibers are synthesized through tuning molar ratio of B/Ti using a facile electrospinning technique. The influences of B content on the phase transition, specific surface area, morphology, and surface valence of TiO2 nanofibers are studied by employing XRD, BET, SEM, and XPS characterization tests. The doping mode and humidity sensing performances for B doping TiO2 nanofibers are also performed in detail. The results show that B is successfully incorporated into the TiO2 lattice using interstitial mode, inducing the increase in cell volume and specific surface area, decreasing grain size. Compared to pristine TiO2 nanofibers, interstitial B doping generates oxygen vacancies and increases the Ti3+ concentration, resulting in an increase in humidity sensitivity. The B-doped TiO2 nanofibers based on the optimum B/Ti molar ratios of 1:4 exhibit high sensitivity, excellent linearity, narrow hysteresis, quick response and recovery time as well as favorable repeatability and stability, which are promising humidity sensing materials. The sensing mechanism is systematically investigated using electrochemical impedance spectroscopy combined with equivalent circuits.