Rituximab, a genetically engineered chimeric monoclonal antibody that specifically binds to CD20, is the first monoclonal antibody approved for the treatment of B-cell lymphoma. It has been shown that rituximab exerts cytotoxic activities through CDC and ADCC, and that it directly induces apoptosis. The CD20 protein has four transmembrane domains (tetraspan structure) and is not internalized following antibody binding, and is not shed or secreted into the circulation. Therefore, CD20 can serve as a target of antibody therapy. As the other anti-CD20 antibodies, there are ofatumumab and obinutuzumab, and clinical development is expected. In addition, histone deacetylate inhibitor or proteasome inhibitor as a new drugs for lymphoma in the future.