The MDM2 oncogene has an important role in human carcinogenesis and has been suggested as a novel target for cancer therapy. Many published in vitro and in vivo investigations have demonstrated that various MDM2 inhibitors including antisense oligonucleotides, siRNA, and small molecule MDM2 inhibitors have antitumor activity in in vitro and in vivo human cancer models, used alone or in combination with cancer chemotherapeutics and radiation therapy. For example, the mixed backbone antisense oligonucleotide developed in our laboratory specifically inhibited MDM2 expression in a dose- and time-dependent manner, resulting in significant antitumor activity in vitro and in vivo. Interestingly, the antisense MDM2 inhibitors have a broad spectrum of antitumor activities in human cancers, regardless of p53 status. These results prompted new investigations into the p53-independent functions of MDM2. This article summarizes the biochemical and molecular studies of the role of MDM2 in the regulation of p21 and E2F1 expression, stability and function, providing evidence for the utility of RNA-silencing technologies, including antisense oligonucleotides and siRNAs.