p53 shows its tumor suppresser activity by inducing cell cycle arrest and/or apoptosis of tumor cells and these activities are in part mediated by p21 cyclin-dependent kinase inhibitor (also called as WAF1, Cip1 and SDI1). Using human aortic vascular smooth muscle cells, here we demonstrate that adenovirus vector expressing p53-induced p21, cell cycle arrest at G1 and G2/M boundary, and accumulation of cells in G1 subgroup. However, adenovirus vector expressing p21 induced only G1 cell cycle arrest. The adenovirus vector expressing p53 was 200 times more cytotoxic to human aortic vascular smooth muscle cells than adenovirus vector expressing p21. These results suggest that adenovirus expressing p53 induces cytotoxicity in human vascular smooth muscle cells by apoptosis and this cytotoxicity can not be fully accounted by p21 induction.