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 °C. When the LnFeO 3 gas sensors are exposed to 100 ppm and acetone at 140 °C, the SmFeO 3 sensor exhibits the largest sensing response (Response = 9.98) compared with LaFeO 3 and NdFeO 3 gas sensors, and the response and recovery times of SmFeO 3 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 .