The present invention describes a method to reduce blood aspartate transaminase level, liver weight, hepatic lipid accumulation and hepatocyte hypertrophy by administering the probiotic bacterium Parabacteroides goldsteinii to a subject. The bacterium Parabacteroides goldsteinii can therefore be used to treat fatty liver disease.本發明提供一種戈氏副擬桿菌(Parabacteroides goldsteinii)之用途,該戈氏副擬桿菌可降低個體血液中天冬氨酸轉氨酶(aspartate transaminase)的含量,並能減少該個體肝臟的重量、降低肝脂肪的蓄積,以及減少肝細胞肥大的現象,因而可利用於脂肪肝疾病之治療以及相關醫藥組成物的製備。