A human monoclonal antibody, 47D11, has been identified that neutralizes both SARS-CoV-2 and SARS-CoV. This antibody targets a conserved epitope on the S1-B receptor-binding domain (RBD) of the viral spike protein, enabling cross-neutralization of both viruses. The antibody binds to the spike protein of SARS-CoV and SARS-CoV-2, inhibiting viral entry into host cells. It effectively neutralizes both viruses in cell culture, with IC50 values of 0.061 µg/ml for pseudotyped VSV infection and 0.19 and 0.57 µg/ml for authentic infection of VeroE6 cells with SARS-CoV and SARS-CoV-2, respectively. The antibody does not block the binding of the spike protein to the ACE2 receptor, suggesting a mechanism of neutralization that is independent of receptor-binding interference. Instead, it may destabilize the prefusion structure of the spike protein, preventing viral entry. The antibody's ability to cross-neutralize SARS-CoV and SARS-CoV-2 is attributed to its binding to a conserved core structure of the S1-B RBD, which is less variable between the two viruses. This antibody has potential applications in the development of diagnostic tests and serological assays for SARS-CoV-2. It may also be used for the prevention and treatment of COVID-19, either alone or in combination with other neutralizing antibodies. The study highlights the importance of targeting conserved epitopes in the viral spike protein for the development of broadly neutralizing antibodies against coronaviruses.A human monoclonal antibody, 47D11, has been identified that neutralizes both SARS-CoV-2 and SARS-CoV. This antibody targets a conserved epitope on the S1-B receptor-binding domain (RBD) of the viral spike protein, enabling cross-neutralization of both viruses. The antibody binds to the spike protein of SARS-CoV and SARS-CoV-2, inhibiting viral entry into host cells. It effectively neutralizes both viruses in cell culture, with IC50 values of 0.061 µg/ml for pseudotyped VSV infection and 0.19 and 0.57 µg/ml for authentic infection of VeroE6 cells with SARS-CoV and SARS-CoV-2, respectively. The antibody does not block the binding of the spike protein to the ACE2 receptor, suggesting a mechanism of neutralization that is independent of receptor-binding interference. Instead, it may destabilize the prefusion structure of the spike protein, preventing viral entry. The antibody's ability to cross-neutralize SARS-CoV and SARS-CoV-2 is attributed to its binding to a conserved core structure of the S1-B RBD, which is less variable between the two viruses. This antibody has potential applications in the development of diagnostic tests and serological assays for SARS-CoV-2. It may also be used for the prevention and treatment of COVID-19, either alone or in combination with other neutralizing antibodies. The study highlights the importance of targeting conserved epitopes in the viral spike protein for the development of broadly neutralizing antibodies against coronaviruses.