Antioxidative components in the methanol extract of the rhizome of Curcuma longa L. were investigated by using our evaluation method based on the air oxidation of linoleic acid. Curcuminoids such as curcumin, 4-hydroxycinnamoyl (feruloyl) methane and bis (4-hydroxycinnamoyl) methane were found to be active components. Curcumin was the most active component and its 50% inhibitory concentrations for the air oxidation of linoleic acid were 1.83×10^-2% (thiobarbituric acid value) and 1.15×10^-2% (peroxide value). These values of curcumin are superior to those of dl-α-tocopherol.