Disclosed are monoclonal antibodies to the HBsAg which are prepared by forming hybridomas between human peripheral blood lymphocyte cells, derived from humans having high titers of anti-HBsAg antibodies, and myeloma cells, cloning the hybridomas and selecting the antibody-producing clones. The monoclonal antibodies react with all the subtypes of the HBsAg and are very effective in diagnosis and treatment of diseases due to the viral infection.