Wet Air Oxidation (WAO) of industrial wastewater in the presence of catalysts provides a potential method for removing high concentration organic chemical wastes from industrial effluents. The oxidation of nitrogen-containing organics tends to form ammonia, oxidation of which is a hardest step among the total oxidation of such chemicals. In this study, an alumina supported ruthenium catalyst was found to exhibit remarkable activities for the oxidation of ammonia. Under a milder operating condition of 453 K, 3.0 MPa, 99% of ammonia (1500 ppm) was removed. The product was dinitrogen exclusively with a small amount of nitrate, which was found to be produced through the nitrite intermediate. The selectivity is significantly affected by the set of reaction conditions such as pH, air feed pressure, temperature and catalyst loading. Based on the result of an optimal experiment, the best set of reaction conditions was found that the selectivity for N2 was 98%. The practical application of this WAO technology was reviewed.