Sm₂O₃/SmFeO₃ mixed powders were applied to a chemo-resistive VOC (volatile organic compound) gas sensor. The sensor response to 30 ppm toluene gas increased with increasing the Sm₂O₃ content up to 30 wt %, but decreased by further adding. The addition of Sm₂O₃ up to 30 wt % also enhanced the catalytic activity for toluene oxidation, as the result of the sensor response. The amount of toluene adsorption increased with increase in the surface Sm concentration. It was concluded that adding Sm₂O₃ increased the amount of adsorbed VOCs, resulting in the enhancement of the sensor response and the catalytic activity. Furthermore, adding Sm₂O₃ remarkably shortened the recovery time from the VOCs to air. For the ethanol sensing, adding Sm₂O₃ was only effective on shortening the recovery time.