In order to clarify the mechanism of action for the antioxidative activity of fluvastatin sodium (FLV, (±)-sodium (3RS, 5RS, 6E)-7-[3-(4-fluorophenyl)-1-(1-methylethyl)-1H-indol-2-yl]-3, 5-dihydroxy-6-heptanoate) and its derivatives, reaction of the corresponding methyl ester of FLV with di-tert-butyl diperoxyxalate was examined, and the corresponding keto derivative was isolated from the reaction mixture. On the basis of this result, it was concluded that the active site is the allylic carbon conjugated with the indole ring.