NiFe2O4 thin film with high porosity based gas sensors had been prepared and their microstructure and gas sensing property were investigated. The sensing layer, consisted of perpendicular overlapped NiFe2O4 chains which were induced by altering magnetic field to self- assemble, had high porosity. The phase character and porous microstructure were characterized by X-ray diffraction ( XRD) and a polarizing optical microscopy. The gas sensing tests results indicated that the sensor presented a high sensitivity to NH3 at 150 degrees C, and was selective to NH3 below 200 degrees C. The large porosity microstructure should benefit the reaction between target gas and sensing material and the detection of low concentration gas at low working temperature. In repeatability tests, the response and recovery time values had only narrow fluctuations. (C) 2015 Elsevier B.V. All rights reserved.