The invention provides an application of bacteroides caccae in treatment or prevention of rheumatoid arthritis or related diseases thereof, and also provides bacteroides caccae containing pharmaceutical compositions, medicaments, foods and feeds. By providing bacteroides caccae for animals, an anti-inflammatory effect can be effectively played, the symptoms such as redness and swelling of joints are effectively improved, and the symptoms of arthritis are obviously relieved, and therefore, the bacteroides caccae can be effectively used for treating or preventing rheumatoid arthritis or related diseases thereof.
