Abstract: The present application provides monoclonal antibodies that specifically bind to the hemagglutinin of avian influenza virus subtype H5, as well as monoclonal antibodies capable of blocking at least 50% of the hemagglutinin binding activity of these monoclonal antibodies. Such antibodies are useful, for example, in the detection, diagnosis, prevention, and treatment of avian influenza virus. Also provided herein are hybridoma cell lines, isolated nucleic acid molecules, and short peptides related to the monoclonal antibodies provided herein, and pharmaceutical compositions and kits containing the monoclonal antibodies provided herein.