In this work,the conformational analyses of staphylococcal enterotoxin B (SEB) after different thermal treatments were carried out by circular dichroism and Laser Raman spectroscopy.The secondary structures of SEB in natural state at 25℃ were composed of 22.6% u-helices,40.4% 1β-sheets,19.2% turns and 17.7% random coils in water solution at the concentration of 0.02mol/L.The content of c-helices gradually descended from 22.6% at 25℃ to 9.6% at 95℃,and disappeared completely at 121℃.In contrast,the content of β-sheets remained relatively stable,and was more than 30.2% at different temperatures.