Absorbance of DPPH in isooctane has been developed to determine the degree of lipid oxidation and antioxidant capacities in lipid systems. Lard with or without addition of sesamol, a free radical scavenger, was thermally oxidized and absorbance of DPPH in isooctane, conjugated dienoic acid (CDA) values, p-anisidine value (p-AV), and sesamol content were analyzed. Changes of DPPH absorbance in early stages of oxidation were highly correlated to the decrease of sesamol content. In later stages of lipid oxidation, formation of radical scavenging compounds from oxidized lipids (RSOLs) played major roles in the decrease of DPPH absorbance. CDA and p-AV did not have good correlations with DPPH absorbance in lard systems. This study clearly shows that the content of free radical scavengers and/or RSOLs influenced the changes of DPPH absorbance, which cannot be determined by conventionally methods like CDA and p-AV methods.