The flaxseed (Linum usitatissimum L.) lignans secoisolariciresinol (SECO) and its diglucoside secoisolariciresinol diglucoside (SDG) are reported to have a number of health benefits including reduction of serum cholesterol levels, delay in the onset of type II diabetes and decreased formation of breast, prostate and colon cancers. The health benefits of SECO and SDG may be partially attributed to their antioxidant properties. To better understand their antioxidant properties, SECO and SDG are oxidized and the major lignan radical- scavenging oxidation products and their formation over time can be determined. Flaxseed lignans act as chain breaking antioxidants in food and biological systems. This indicates that flaxseed lignans may be useful as alternative natural antioxidant preservatives and may be applicable in this role in vegetable oils and in other oil-based foods to provide additional health benefits as antioxidant or antiestrogenic compounds.