The treatment of Non-Hodgkin's lymphoma (NHL) was revolutionized by the approval of rituximab in 1997. Rituximab is a CD20-directed monoclonal antibody (mAb). Despite the great success of rituximab in the treatment of B-cell NHL, the urgent need is to enhance the efficacy due to the markedly variable patient responses. Hence elucidating the molecular mechanisms of rituximab's anti-cancer effect is of great significance. In the past decade the atomic force microscopy (AFM) has proven to be a powerful tool for characterizing the morphological properties and measuring the physiological interaction forces of single cells and single molecules under native conditions. In this work, the AFM single-molecule force spectroscopy(SMFS) was applied to quantitatively measure the CD20-rituximab binding force on Burkitt's lymphoma patient bone marrow cells. The experimental results will facilitate further investigation of the molecular mechanisms of rituximab's anticancer effect.