The antioxidative activities of wasabi (Eutrema wasabi MAXIM.) root, stem, and leaf extracts were evaluated by several methods. The wasabi stem extract was found to be a strong antioxidant when tested by the TBA method using deoxyribose as the substrate, whereas the HPTLC assay using linolenic acid as the substrate indicated that the activity of the leaf extract was greater than those of the stem and root extracts. All three extracts showed strong-OH radical scavenging activity when tested by the ESR method. Superoxide scavenging activity was extremely high in the leaf extract, whereas the stem and root extracts did not show any appreciable effect. These results suggest the occurrence of different antioxygenic principles in the leaf and stem of wasabi. As most of the wasabi leaf and stem has not been utilized so far, these findings will contribute to the total utilization of wasabi plants.