The present invention provides a method of preventing or treating obesity by administering the probiotic bacterium of a novel Parabacteroides goldsteinii strain to the subject in need. The novel Parabacteroides goldsteinii strain is derived from the gastrointestinal tract of an individual and has better aero-tolerance and better acid-tolerance therefore it has better environmental tolerance to adapt to different living environments. The novel Parabacteroides goldsteinii strain not only can effectively prevent the weight gain of the individual, but also can effectively slow down the weight gain of the obese individual； therefore, the novel Parabacteroides goldsteinii strain of the present invention can be used for preparing a pharmaceutical composition for prevention and/or treating obesity.
