Bacteroides uniformis (B. uniformis) is an obligate anaerobic Gram-negative bacteria, it belongs to Bacieroides spp.. It is an important component of the normal gut microbiota in human body and rarely causes opportunistic infection in clinical practice. Currently, there is no consensus on the clinical characteristics, diagnosis, treatment, and prognosis of infection caused by B. uniformis, and the resistance of anaerobic bacteria is difficult to be detected. This article reports a case of a lung tumor patient who developed diarrhea and bloodstream infection due to B. uniformis after chemotherapy. After empirical anti-infective treatment with cefoperazone/sulbactam, the patient recovered and was discharged from hospital. This paper aims to improve clinical understanding on infection caused by opportunistic pathogens in the gut, and provide reference for timely diagnosis and effective treatment.