Influenza A viruses are a major threat to human health and inflict a significant public health challenge worldwide. Hemagglutinin (HA) is the main contributor to the infectivity of the virus and is a potential target for the development of antiviral therapeutic agents. The stem region of HA, which has been shown to be conserved, is the primary target in the development of antibody-based therapeutic strategies and preventive tools. Here, we confirmed the neutralizing activity and prophylactic efficacy of murine monoclonal antibody PR8-25 as well as Western blot analysis of different influenza virus strains. Then, we identified the epitope of PR8-25, 328-LRMVTGLRNIPS-339, by phage-displayed 12-mer random peptide library. The identified epitope targeted in the stem region of HA, specifically at the C-terminal of the HA1 fragment. This result suggest that the identified epitope may be a potential basis for antiviral drugs and stem-based universal influenza vaccines.