A catalyst which can maintain excellent catalytic activity and excellent durability for a long period when used in a wet oxidation treatment of waste water, and a method for the wet oxidation treatment of waste water using the catalyst, are provided. Also provided is a novel method for treating a waste water containing nitrogen-containing compounds, in which a catalyst of a lower catalyst cost is used, a waste water containing nitrogen-containing compounds can be treated with high purifying performance, and superior purifying performance can be maintained. The catalyst for waste water treatment contains, as a component A, an oxide of at least one element selected from the group consisting of iron, titanium, silicon, aluminum, zirconium and cerium, and as a component B, at least one element selected from the group consisting of silver, gold, platinum, palladium, rhodium, ruthenium and iridium, wherein at least 70% by mass of the component B is present in the region within 1000 µm from the outer surface of the oxide of the component A, the average particle size of the component B is 0.5 nm to 20 nm, and the solid acid content of the oxide of the component A is 0.20 mmol/g or greater. he method for treating waste water includes treating a waste water containing nitrogen-containing compounds in the presence of an oxidizing agent, at a temperature equal to or higher than 100°C and lower than 370°C under the pressure conditions so as to keep the waste water in liquid phase, by using a catalyst which converts a nitrogen-containing compound into ammoniacal nitrogen (pre-catalyst) on the upstream side in the flow direction of the waste water, and a catalyst on the downstream side for treating an ammoniacal nitrogen-containing waste water (post-catalyst) on the downstream side.