Disclosed is a monoclonal antibody capable of inducing a specific biological reaction through the binding of the monoclonal antibody to a CD20 antigen on the surface of a cell. A monoclonal antibody having a high binding affinity to an extracellular epitope of a CD20 antigen and also having biological activities including a cell growth inhibitory activity is cloned. The monoclonal antibody is chimerized or humanized to develop a therapeutic agent for a disease in which B cells are involved.本發明提供一種藉由結合於細胞表面的CD20抗原，誘導出特異性生物學反應之單株抗體。選殖對於CD20抗原的細胞外表位具有強結合親合性，且具有細胞增殖阻礙活性等生物學活性之單株抗體。且藉由嵌合體化或人類化該單株抗體而開發出對於與B細胞相關疾病之治療藥。
