Peanut allergen Ara h 2 was extracted from peanuts and was identified by SDS-PAGE and MALDI-TOF-MS. Effect of heat treatment on the antigenicity and structure of Ara h 2 was measured by indirect ELISA, CD, fluorescence and UV absorption spectra. The results showed that the antigenicity of Ara h 2 had a slight increase after being heated at 55 or 70 ℃, while above 85 ℃ the antigenicity decreased significantly, and the antigeicity of Ara h 2 decreased with increasing temperature. The CD showed that the secondary structure of Ara h 2 was changed after heat treatment. The ANS fluorescence probe emission spectra analysis demonstrated that the heat treatment induced an increase in surface hydrophobicity of Ara h 2. The UV absorption spectra showed that the absorption maximum wavelength was increased when Ara h 2 was heated except the sample heating at 50 ℃ for 30 min. So the changes in conformation of Ara h 2 lead to the antigenicity degression.