O⁶-methylguanine-DNA methyltransferase (MGMT) is a specific DNA repair protein that exist in cells and tissues from bacteria to mammalias. The function of the repair protein is to catalyzing and transfering the alkyl group from the O⁶ position of guanine of DNA to an internal cysteine residue of MGMT protein which repairs the lesion by reversion the guanine of DNA. Therefore the proper expression of MGMT is useful to repair O⁶-methylguanine-DNA adducts formed by the induction of alkyl agents. The amount and activity of MGMT are not only regulated by various factors at genetic level, but also associated with the directly effects of some drugs. It has important significance to regulate the activity of MGMT in the cells during the prevention of tumor-geneses and overcoming the drug resistance or marrow toxicity.