Antioxidant activities of phenolic compounds have been extensively explored, but the determinant factors underlying their mechanisms of action remain to be elucidated. In the present work, a series of phenolic compounds (hydroxylated connamic, benzoic acid, and polyphenol) were studied for their protection against lipid peroxidation (LPO) in two model experiments, pre-emulsified linoleic acid system and phosphate buffered linolenic acid system. The mechanisms of action as well as activity determinants were investigated by computational chemistry and multiple-linear regression analysis. Upon elucidating the LPO inhibition properties and the relationship between their structural natures and antioxidant activities (SAR), a fairly satisfactory multidescriptor quantitative SAR model was derived, which extended our understanding of LPO inhibition mechanisms and should be valuable in assessing or predicting the anti-LPO activity of phenolic antioxidants. (C) 2003 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 92:475-484, 2003.