This study was carried out to investigate whether water extract of Sagunja-Tang and its composing herbs have the inhibitory effects on cytotoxicity and lipid peroxidation induced by oxidant in rat renal cortical slices. Cytotoxicity was estimated by measuring lactate dehydrogenase (LDH) activity and lipid peroxidation was examined by measuring malondialdehyde (MDA). a product of lipid peroxidation. When rat renal cortical slices were treated with tert-butylhydroperoxicle (t-BHP) of 1 mM and water decocted herbs. LDH release from the slices was inhibited in dose dependent manner at low concentrations of herbs. It shows that herbs can reduce cytotoxicity, but overdose of herbs can be toxic to the slices. And MDA measurements show each herb has its own activities of preventing cytotoxicity from oxidants. So further studies should be followed to make clear the mechanisms of anti-oxidative effects of herbs.