Technical Abstract: Antipolymerization activities of lignans including nordihydroguaiaretic acid, (+)-pinoresinol, (-)-secoisolariciresinol, enterodiol, two sesame lignans (sesamol, sesamin), and four model compounds were investigated for soybean oil at frying temperature (180 °C). The heated samples were analyzed by GPC (gel permeation chromatography) for polymerized triacylglycerols and 1H NMR for monitoring decrease in peak intensities of bisallylic protons and olefinic protons. The heating test results were compared with the radical scavenging abilities toward ABTS (2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)) radical to understand the relationship between radical scavenging ability at room temperature and antipolymerization activity at 180 °C. It was found that the antipolymerization activity of a lignan at frying temperature cannot be predicted by only the radical scavenging ability at room temperature. Lignans tested in this research showed antipolymerization activities, but not as strong as 200 ppm TBHQ (tert-butylhydroquinone) with the same equivalent of phenolic moiety (0.0012 meq/g). At higher concentrations, however, sesamol, nordihydroguaiaretic acid and (+)-pinoresinol showed better antipolymerization activity than the legally limited amount of TBHQ (200 ppm, 0.0012 meq/g). Therefore, this research showed that a proper concentration of a lignan, the non-toxic natural antioxidant can replace synthetic antioxidants providing not only better antioxidation activity but also health benefits.