Abstract: Polo-like kinases 1 is a highly conserved serine / threonine protein kinase that plays a key role in regulation of mitosis. In about 80% of human tumors,of various origins,PLK1 is over expressed;while,PLK1 mRNA is often absent in the normal tissues. Meanwhile,over-expression of PLK1 is associated with a poor prognosis in several tumor types and a lower overall survival rate. PLK1 inhibitors can interfere with different stages of mitosis,such as centrosome maturation,spindle formation,chromosome separation,and cytokinesis,inducing mitotic chaos and severe perturbance of cell cycle progression,which eventually lead to tumor cell death. Therefore,PLK1 is one of the most attractive and promising targets for antitumor drug development. This review introduces PLK1 inhibitors of different structures in preclinical or clinical development.