Polycyclic aromatic hydrocarbons ( PAHs) are ubiquitous environmental pollutants, whose carcinogenicity is determinated.The mechanism of their carcinogenicity: PAHs are able to combine with aryl hydrocarbon hydrocarbon receptor ( AhR ) , resulting in some toxicity and carcinogenicity.AhR is a ligand-dependent activation transcription factor, which is activated by a large variety of ligands, regulating the expression of a series of gene involved in metabolism, and participating in important biological processes, such as singal transduction, cell proliferation,differentiation and apoptosis,and so on.Besides, it's closely related with the tumor development.Thus, it will provide a new approach for cancer prevention and treatment to study the role of PAHs and AhR in the development of tumor.