To provide a method for decomposing ammonia with nitrifying bacteria, which has become difficult to be metabolized due to a disease and so on by making the inside of the intestine under an anaerobic environment temporarily an aerobic state.

In the method for decomposing ammonia in intestine, decomposition of ammonia is urged by putting nitrifying bacteria which exist from start in intestine or have been injected from the outside in an aerobic condition by injecting ultrafine bubbles of oxygen (micro nanobubbles) with drinking or enema in intestine, and in addition adding oil and fat.