Abstract: Endoreduplication is a special phenomenon of nuclear polyploidization that results from lacking of mitosis. When cell cycle repeats S-phase and can not enter M-phase, endoreduplication occurs. The caracter of endoreduplication is the inactivation of MPF and oscillatory activation of CDKs. Endoreduplication has been observed in many plant and animal species, and is documented to appear more frequently in tissues with high metabolic activity and highly differentiated cells. Therefore, it may play an important role in cell proliferation and cell enlargement. This paper has reviewed recent progress in the study of the molecular mechanism and regulators of endoreduplication in representative plants and mammals.