<p>Bacterial outer membrane vesicles (OMVs) were previously considered merely as waste products of bacterial metabolism. But its inherent stability, immunogenicity, ability to be highly regulated, and targeting potential are turning them into a platform with revolutionary potential in tumor drug delivery. Tumor remains a major challenge in medicine. Even though traditional therapies are effective to some extent, they are often accompanied by intolerable side effects. Furthermore, conventional treatments have low targeting efficiency, and tumor cells almost always develop resistance to them. OMVs are naturally tiny vesicles released by Gram-negative bacteria. They possess the ability to deliver drugs very efficiently and at the same time stimulate the host immune system. As a result, they can overcome limitations such as poor targeting and drug resistance. OMVs have huge potential not only in tumor therapy but also in the development of vaccines and drug delivery systems. Nevertheless, reviews focusing solely on their role in tumor drug delivery systems are still quite rare. This review thoroughly analyzes the immunological basis of bacterial OMVs, the engineering strategies, and their antitumor applications with a focus on how their innate immunogenicity and highly customizable features can be exploited to develop precision antitumor platforms. It essentially offers a comprehensive and systematic theoretical framework for realizing and elevating the latent use of bacterial OMVs in tumor therapy.</p>