The invention provides an application of clostridium nexile in treating or preventing rheumatoid arthritis or related diseases thereof, and also provides a pharmaceutical composition, a medicament, a food and a feed containing the clostridium nexile. By providing the clostridium nexile for animals, an anti-inflammatory effect can be effectively brought into play, the symptoms of rubefaction and swelling of joints can be effectively improved, and the symptoms of arthritis can be obviously relieved, so that the clostridium nexile can be effectively used for treating or preventing the rheumatoid arthritis or the related diseases thereof.