Abstract: Peanut protein isolate (PPI) was oxidized by free radicals and reactive oxidation products released by lipoxygenase-catalyzed linoleic acid. Carbonyl content, free sulphydryl content, particle size distribution, surface hydrophobicity, solubility and intrinsic fluorescence were determined to evaluate effect of oxidation on the structure of PPI. Results showed that, with increasing content of linoleic acid, the carbonyl content first increased then slightly decreased, the free sulfhydryl content decreased, and the surface hydrophobicity first increased then decreased, which reflected change in the structure of PPI after oxidation. Changes in the particle size distribution and solubility indicated the condition of PPI aggregates, and difference in the maximum emission wavelength indicated change of the tertiary conformation of PPI. All these showed that lipid oxidation could induce protein aggregation, leading to significant change in the structure of PPI.