Bi(3.25)Ln(0.75)Ti(3)O(12) (Ln= La, Ce, Nd, Sm) (BLnT) nanofibers are prepared by the electrospinning method and characterized by X-ray diffraction, field-emission scanning electron microscopy, and X-ray photoelectron spectroscopy. The humidity sensors based on BLnT nanofibers are fabricated and their humidity sensing properties are measured at room temperature within the relative humidity (RH) range of 11-95%. The optimum working frequencies of all BLnT humidity sensors are 10 Hz, and the impedance variation of Bi3.25Sm0.75Ti3O12 (BST) humidity sensor is about six orders of magnitude within the whole humidity range from 11% to 95% RH, which is larger than it of other BLnT humidity sensors. The response time of BST humidity sensor is about 3 s and the maximum humidity hysteresis is 3% RH. The results indicate that the BST humidity sensor is of the best humidity sensitivity compared to other BLnT humidity sensors due to the low Ln-O binding energy and large lattice distortion. We expect that our work may offer the guidelines for the investigation of the relationship between binding energy and humidity sensing properties.