The effect of ginseng sapogenins, aglycone parts of ginsenosides, against oxidative damage by radical generator, 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH), in renal epithelial LLC-PK 1 cells was investigated to identify the structural characteristics of sapogenins to have renoprotective effects. Of the tested sapogenins, Δ 20(21) -protopanaxatriol showed the strongest protective effect against the AAPH-induced LLC-PK 1 cell damage. Based on the structure and stronger activity of Δ 20(21) -protopanaxatriol than the other sapogenins, the hydroxyl group in C-6 and double bond in C-20(21) position were important for renoprotective effect of sapogenin against oxidative stress.