This study was to investigate the cell cycle arrest effect and its mechanism of Radix Aconiti (RA) extract in HepG2 human hepatoma cells. We used the Flow Cytometer to investigate the effects on cell cycle arrest in RA extract-treated HepG2 cells. And protein levels involved in cell cycle progression such as p53, p21, and p21 are detected by Western blotting method. RA extract induced cell cycle arrest as confirmed by increase of G0/G1 cell population, and the mechanisms were related with up-regulation of p53, p21, p27 protein expressin in HepG2 cells. These results suggest that RA may be a valuable agent for the therapeutic intervention of human hepatomas.