Effects of ethanol injection on NOx removal performance in an ozone advanced oxidation process were investigated based on a scale-up reaction system. Experimental results showed that the introduction of ethanol in simulated flue gas could enhance NOx removal performance greatly in the O-3-ethanol-NOx system. With an initial NO concentration of 400 ppm in flue gas at 150 degrees C, the injection of 200 ppm O(3 )could oxidize approximately half of NO into NO2. When further introducing -150 ppm ethanol vapor in flue gas, the outlet NO concentration would drop sharply to similar to 68 ppm while outlet NO2 concentration would drop down to similar to 165 ppm at the same time. This enhancement effect was ascribed to a synergistic reaction between O-3, ethanol, and NOx in the gas phase. The gas reaction products were analyzed by using gas chromatography-mass spectrometry, and some kinds of nitro-compounds, such as nitroso methane, nitromethane, nitric acid methyl ester, and nitric acid ethyl ester, had been found. It is implied that some complex reactions might occur between ethanol and O-3 at the presence of NOx in which a large number of organic radicals and hydroxyl radicals had been produced. In addition, the effects of key operating parameters on NOx removal performance were investigated through comparing the changes in the NQ concentration between O-3-NOx and O-3-ethanol-NOx systems, and the related reaction mechanism had also been discussed.