Peanut protein isolates (PPI) was oxidized by peroxyl radicals derived from 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) and the secondary structure of oxidized PPI were evaluated. Structural changes of PPI were elucidated using Fourier transform infrared spectroscopy (FTIR). Fourier deconvolution combined with iterative curve fitting was used to analyze the amide I of FTIR. After deconvolved amide I FTIR bands, ten major bands associated with conformation of proteins were distinctly observed. Changes in the bands at 1 618 cm^-1 and 1 682 cm^-1, which arise from the aggregated intermolecular β-sheets, indicated that protein aggregation occurred during PPI oxidation. Quantitative analysis was obtained by iterative curve fitting. The results showed that there was an increase in β-sheet structure and random structures accompanied by a decrease in turns and alpha helix, with the increase of oxidizing agent (AAPH<3.00 mmol/L). Higher level oxidation (5.00 and 10.00 mmol/L) would induce fragmentation through direct breakage of peptide bonds, resulted in changes in the secondary structures. The hydrogen bonds and hydrophobic interactions played an important role in the formation of PPI aggregates.