is an important bacterial fish pathogen that can cause vibriosis extensively in economically-important fish including Anguilla anguilla, and in China. In our previous studies, we have carried out the epidemiological work of O1, O2, and O3 serotype strains are prevalent in marine fish farms. Vaccination is proven to be a safe and efficient route to prevent and control vibriosis. However, no commercial vaccine is available in China. In this study, the antibody persistence and immune protection duration of a inactivated bivalent vaccine based on O1 and O2 serotype strains were evaluated in turbot ( formalin-inactivated bivalent vaccine was prepared using O1 serotype VAM003 and O2 serotype VAM007 strains. Groups of turbot were injected intraperitoneally with three dosages of vaccine preparation, i.e, 10⁷ cells/ind, 10⁸ cells/ind, and 10⁹ cells/ind. At 3 d, 7 d, 14 d, 30 d, 60 d, 90 d, 120 d, and 150 d after injection, each immunized fish group was evaluated for their serum-antibody titers against VAM003 and VAM007 using a serum-agglutination test, and the relative percent survival (RPS) was evaluated by challenge with a 10 LD₅₀ (50% lethal dose) of VAM003 or VAM007. The results showed that specific antibodies against VAM003 and VAM007 were noticeably induced in the immunized fish as early as 7 d post-immunization, and an RPS of 27%-60% was detected in these fish. Specifically, the induced VAM003 antibody persisted in three dosage fish groups for at least 90 d for 10⁷ cells/ind, 150 d for 10⁸ cells/ind, and 150 d for 10⁹ cells/ind, respectively, while anti-VAM007 persisted in each of three dosage fish groups for more than 150 d. The immune protection duration for each of the three dosage groups all exceeded 150 d. With an RPS of more than 75% as an effective immune protection, the effective immune protection duration against O2 serotype cells/ind fish group, 14-120 d for 10⁸ cells/ind group, and 14-150 d for 10⁹ cells/ind group, respectively, while the effective immune protection duration against O2 serotype were 14 d-60 d for 10⁷ cells/ind group, 14-120 d for 10⁸ cells/ind group, and 14-120 d for 10⁹ cells/ind group, respectively. We also analyzed the relationship between serum antibody titer and RPS of bivalent vaccine. When the serum antibody titer was over 1:40 for the O1 serotype and 1:160 for the O2 serotype, the corresponsive RPS to O1 or O2 serotype were all over 75%. These results suggest that the inactivated bivalent vaccine could provide effective immune protection for turbot, and the data of antibody persistence and immune protection duration obtained in this study will provide support for clinical trials of this vaccine.