Abstract: Oral bacterial vaccines are currently a hot topic in vaccine research, owing to such advantages as ease of administration, enhanced patient compliance, and their ability to induce mucosal immunity, humoral immunity, and cellular immunity simultaneously. Nonetheless, the stability and efficacy of these vaccines are hindered by the complexities of the gastrointestinal environment and the absence of efficient delivery systems. In recent years, the rapid development of synthetic biology and materials science technologies has provided opportunities for addressing the above challenges. This review offers a comprehensive overview of the immunological mechanisms underlying oral bacterial vaccines, recent research advancements concerning whole bacteria and bacterial components-based vaccines, innovative engineering strategies adopted in their development, and their applications in tumors and viral infection. In addition, several promising strategies for the delivery of oral bacterial vaccines have been thoroughly discussed, aiming to provide some valuable insights for future research in this important field.