Abstract: The Polycomb group（PcG）protein family is a group of gene regulatory elements playing roles in embryonic development，which functioning in tow distinct protein complexes termed Polycomb-repressive complex 1（PRC1） and Polycomb-repressive complex 2（PRC2）. EZH2 is the catalytic subunit of PRC2，which is a highly conserved histone methyltransferase that targets lysine-27 of histone H3. Most studies on human tumors show that EZH2 is over-expression in a variety of tumors，including prostate and breast. Although the mechanism of EZH2 with cancer progression is not determined，functional link between EZH2-mediated histone methylation and DNA methylation indicate which involved in the gene silencing machinery implicated in tumor suppressor loss. The authors review the basic molecular biology of EZH2 and the findings of EZH2 in different cancers. And also discuss EZH2 connections to other epigenetic modifying enzymes，as well as the consequences of EZH2 overabundance and its potential roles in tumorigenesis.

Key words: Epigenesis, genetic, Gene silencing, DNA methylation, Neoplasms, Enhancer of zeste homologue 2