The COVID-19 pandemic caused by SARS-CoV-2 is still prevalent around the world. Vaccine development, promotion, usage are key means to prevent COVID-19. Nuclearcapsid protein (NP), as the main structural protein of SARS-CoV-2, is a potential candidate target for vaccine development. Flagellin B (FlaB) has been used as an immune adjuvant to enhance the immunogenicity of antigens. In this research, we analyzed the immunogenicity of NP and a NP-FlaB fusion protein. Firstly, the NP, NP-FlaB fusion protein were expressed and purified by the E. coli system; then the BALB/c mice were immunized with the antigens by subcutaneous or intranasal route; the NP-specific serum IgG, mucosal IgA and cytokine secreting T cell responses were analyzed. The results showed that: one-time subcutaneous immunization of NP or NP-FlaB fusion protein was sufficient to elicit robust anti-NP serum IgG antibody response and IL-4 secreting T cell response, and no significant differences were observed between NP and NP-FlaB fusion protein. However, when inoculated by the intranasal route, NP-FlaB fusion protein introduced significantly higher NP-specific serum IgG titer, as well as the higher mucosal IgA titer at the resident of lung. The overall results showed that, SARS-CoV-2 NP and NP-FlaB fusion protein are highly immunogenicity, NP-FlaB fusion protein can induce mucosal immune response, both of them are effective candidates for SARS-CoV-2 vaccine. In summary, our research on the immunogenicity of NP and NP-FlaB of SARS-CoV-2 provided a new idea and reference for the subsequent development of SARS-CoV-2 vaccine based on NP.