Abstract: Cell- cycle deregulation leading to excessive cell proliferation is an important mechanism of human tumorigenesis. CDK6 and CDK 4 have been found to be significant regulators of cell cycle, particularly in promoting cell- cycle progress. Moreover, these proteins are usually overly active in most tumors and closely related to tumor development. Recently, research has confirmed CDK4/6 as prospective targets for cancer therapy. However, the mechanism of excessive CDK6 activation leading to tumorigenesis is not completely understood. Therefore, further understanding of the role of CDK4/6 in cell-cycle regulatory pathways and cell differentiation is essential, as well as their overexpression in different types of tumors. This information will elucidate the mechanisms of tumor development and treatment. Therefore, this review intends to discuss the structure and biological function of CDK 6, the role and mecha-nism of CDK6 in carcinogenesis, and the clinical application of CDK 6 inhibitors.