Recently, studies on natural source antioxidants have become increasingly active in various fields. Among analytical methods for assessment of antioxidant activity, the DPPH, ABTS, and TBA assays have become quite popular in natural antioxidant studies. One of the reasons is that these methods are simple to use and highly sensitive. In particular, DPPH and ABTS assays are based on the theory that a hydrogen donor is an antioxidant. The antioxidant effect can be easily evaluated by following the decrease of specific UV absorption and the results are usually expressed in terms of Trolox equivalent antioxidant capacity (TEAC). The TBA assay has been commonly used for measurement of lipid oxidation in some foods and biological systems. Because the colored complex is formed by the TBA-malonaldehyde interaction, the TBA value can be evaluated using a UV spectrophotometer or HPLC. However, the TBA-malonaldehyde complex is very unstable and often is either not detected in many oxidized lipids or is a minor product of secondary oxidation. As a result of these defects, numerous studies are ongoing.