To investigate the possible mechanism of Biochanin A-mediated cell cycle arrest and apoptotic effect on the lung cancer cells, the expressions of cell cycle-related proteins (namely, cyclin A, P21, and CDK2) and apoptosis-related proteins (namely, Caspase-3, Bax, and Bcl-2) were assessed by Western blot analysis. The gene discussed is CCNA2; the disease is lung cancer.