LnFeO(3) (Ln = La, Nd, and Sm) nanofibers are synthesized by the electrospinning, and characterized by X-ray diffraction, field-emission scanning electron microscopy, and X-ray photoelectron spectroscopy. For investigating the effect of lanthanide on acetone sensing properties of LnFeO(3) nanofibers, the side-heating gas sensors based on LnFeO(3) nanofibers are fabricated and measured at different temperatures and acetone concentrations. The optimal working temperatures of the LnFeO(3) gas sensors are all 140 degrees C. When the LnFeO(3) gas sensors are exposed to 100 ppm and acetone at 140 degrees C, the SmFeO3 sensor exhibits the largest sensing response (Response = 9.98) compared with LaFeO3 and NdFeO3 gas sensors, and the response and recovery times of SmFeO3 sensor are about 17 and 16 s, respectively. The results indicate that the lanthanides have an impact on the acetone sensing properties of LnFeO(3), and the lanthanide with low binding energy of the Ln-O bond is beneficial for improving the acetone sensing properties of LnFeO(3).