The ubiquitin protein ligase (E3) MDM2 (Murine double minute 2) possesses oncogenic activities. Overexpression of this protein enhances degradation and inactivation of the tumor suppressor p53. At least 7% of all human tumors exhibit inappropriate amplification of mdm2, whereas p53 gene remains in its wild-type configuration. This indicates that MDM2 may function in the p53-independent manner to promote tumorigenesis. Considering the critical role of MDM2, this review summarizes the current mechanisms and progress on MDM2 regulation in levels of gene control, mRNA transcription, post-translational modification, and interaction proteins.