Triterpenoids are implicated in the chemoprevention of various cancers. Current challenge is to define the molecular mechanism underlying the chemopreventive activity of triterpenoids. This study was designed to characterize the intracellular proteins regulated by astragaloside IV, the major active triterpenoid in Radix Astragali. Upon the treatment with astragaloside IV, human hepatocellular carcinoma HepG2 cells were evaluated for the colonogenic survival and anchorage-independent growth. The cellular proteins of treated and untreated cells were resolved by 2-D polyacrylamide gel electrophoresis. The protein spots mostly altered by drug treatment were identified by mass spectrometry and subsequently verified by Western blotting using specific antibodies and RT-PCR technique using specific DNA primers. We found that astragaloside IV attenuated the colonogenic survival and anchorage-independent growth of cancer cells. Based on the proteomic profiles, top 14 upregulated and 13 down-regulated protein spots were subjected to mass spectrometric analysis. As an example, Vav3.1 belongs to the oncogene Vav family, which is implicated in tumorigenesis. Vav3.1 expression was down-regulated by astragaloside IV in a dose- and time-dependent manner. Down-regulation of Vav3.1 was highly correlated with the suppression of cell malignant transform. Thus, astragaloside IV may elicit anticancer activity via down-regulating the expression of oncogenes such as Vav3.1.