NOVELTY - Preparation of ethanol gas sensor element involves preparing dry gel precursor by dissolving lanthanum nitrate nonahydrate and ferric nitrate hexahydrate in deionized water, then adding citric acid, heating, then adding polyethylene glycol and stirring, heating, milling powder, sintering and obtaining nano lanthanum-iron oxide powder, adding powder in agate mortar, then adding glass fibers, then dripping terpineol and grinding to paste form, coating paste on both sides of electrodes, drying and sintering, and welding electrode lead together on sensor base.    USE - Preparation of sensor element used for sensing ethanol gas, methane, acetone, carbon dioxide and glycerol (all claimed).    ADVANTAGE - The method efficiently and economically provides ethanol gas sensor element having high sensitivity of 138 in 1000 ppm at working temperature of 140 degrees C. The gas sensor element is economical and environmentally-friendly, and has reduced working temperature and reduced response recovery time of 1 second and 1.5 seconds.    DETAILED DESCRIPTION - Preparation of ethanol gas sensor element involves preparing dry gel precursor by dissolving lanthanum nitrate nonahydrate and ferric nitrate hexahydrate in deionized water, then adding citric acid such that molar ratio of precursor solution and citric acid is 1:2, heating mixed solution in water bath at 70-80 degrees C, then adding polyethylene glycol PEG-6000 and stirring continuously, adding dry gel into a crucible, heating to remove organic substances, milling resulting powder in muffle furnace, sintering at 590-610 degrees C for 2 hours and obtaining nano lanthanum-iron oxide powder, adding 0.1 plus minus 0.05 g powder in agate mortar, then adding 0.025 plus minus 0.005 g glass fibers, then dripping 0.2-0.3 ml terpineol and grinding to paste form, coating paste on both sides of electrodes, drying in muffle furnace and sintering at 590-610 degrees C for 2 hours and welding electrode lead together on a sensor base. The stoichiometric ratio of lanthanum and iron in precursor is 1:x (where x is 0.7 to less than 1).