The highly pathogenic avian influenza H5N1 virus clade 2.3.4.4b has been spreading globally 30 since 2022, causing mortality and morbidity in domestic and wild birds and mammals, including 31 infection in humans, raising concerns about its pandemic potential. We aimed to generate a panel 32 of anti-hemagglutinin (HA) human monoclonal antibodies (mAbs) against the H5 protein of clade 2.3.4.4b. H2L2 Harbour Mice® 33 , which express human immunoglobulin germline genes, were 34 immunized with H5 and N1 recombinant proteins from A/mallard/New York/22-008760-007- 35 original/2022 H5N1 virus, enabling the generation of human chimeric antibodies. Through 36 hybridoma technology, sixteen full human mAbs were generated, most of which showed cross37 reactivity against H5 proteins from different virus variants. The functionality of the sixteen mAbs 38 was assessed in vitro using hemagglutination inhibition and microneutralization assays with 39 viruses containing a clade 2.3.4.4b HA. Fourteen out of the sixteen mAbs neutralized the virus in 40 vitro. The mAbs with the strongest hemagglutination inhibition activity also demonstrated greater 41 neutralizing capacity and showed increased protective effects in vivo when administered 42 prophylactically or therapeutically in a murine H5N1 challenge model. Using cryo-electron 43 microscopy, we identified a cross-clonotype conserved motif that bound a hydrophobic groove on 44 the head domain of H5 HA. Akin to mAbs against severe acute respiratory syndrome coronavirus 45 2 (SARS-CoV-2) during the coronavirus 2019 (COVID-19) pandemic, these mAbs could serve as 46 important treatments in case of a widespread H5N1 epidemic or pandemic.