It is known that a close relationship exists among oxidative damage, senescence, and aging. Water dropwort (Ostericum sieboldii Miq. Nakai) and Sedum (Sedum sarmentosum Bunge) are popular green vegetables in Korea and are reported to have strong antioxidative activity. We investigated whether dropwort and Sedum have the potential to prevent aging using H(2)O(2)-induced prematurely senescent human diploid fibroblasts (HDFs). Dropwort and Sedum had similarly high contents of polyphenols, but dropwort had a flavonoid content about twofold higher than that of Sedum. Exposure of young HDFs to H(2)O(2) induced G2/M cell cycle arrest, positive senescence-associated (SA) beta-galactosidase (beta-gal) staining, and elevated p53, p21, and p16 protein levels. However, cotreatment with dropwort or Sedum ethanol extract significantly lowered p53, p21, and p16 levels and intracellular reactive oxygen species levels and attenuated the cell cycle arrest compared with H(2)O(2)-alone treatment. Interestingly, the increase in p16 level was prevented more quickly and clearly by dropwort treatment than Sedum treatment. The number of SA beta-gal-positive cells at 7 days after treatment was significantly reduced in dropwort-treated cells compared to H(2)O(2) alone-treated cells, whereas it was slightly reduced in Sedum-treated cells with no significance. In conclusion, dropwort showed a potential anti-senescence activity in H(2)O(2)-treated HDFs, which might be mediated by reducing p16, p21, and p53 levels and oxidative stress.