This chapter describes the basic characteristics of oral tumor cells，which have three marked characteristics:immortality，migration and no contact inhibition as cancer cells in other sites.Oral cancer is formed under the interaction of internal and external factors.Up to date studies show that oral cancer is the outcome of chromosomal genetic changes that result in cell signaling and cell cycle disorders，inhibition of apoptosis，and prolongation of cancer cell survival.Cancer markers are useful for cancer diagnosis，prognosis and evaluation of treatment efficacy，and multiple markers such as PCNA，Mib-1，Cyclin D1and CENP-F reflecting oral precancerous lesions and oral tumor cells have been found，but most tumor markers in blood and especially in saliva are not enough sensitive and accurate to detect.Oral tumor metastasis is involved in multiple signaling-associated molecules such as TGF-β，cyclooxygenase-2and nitric oxide synthese（NOS）and vascular endothelial growth factor（VEGF）.