Abstract: Bacterial extracellular vesicles (BEVs), bacteria-derived extracellular vesicles, are key intermediates of bacteria-bacteria and bacteria-host interactions. They are a "double-edged sword". On one hand, they play a negative role in the onset and progression of various diseases, including intestinal inflammatory disease, neurological disease, liver disease, metabolic disease, autoimmune disease and cancer. On the other hand, they play a positive role as potential biomarkers, vaccines, antitumor agents. The application of BEVs may provide novel strategies for the diagnosis and treatment of diseases. However, research on BEVs is still in its infancy, and challenges remain in vesicle isolation techniques, disease diagnostic specificity, optimization of vesicle storage and transport. Thus rigorously designed clinical studies are required to verify their diagnostic and therapeutic value.