The fragment Aβ(25–35) of the Alzheimer's amyloid β -peptide, like its full-length peptide Aβ(1–42), has shown neurotoxic activities in cultured cells. The conformational preference of this important peptide is examined here in solution, gel, and film states (obtained with organic and aqueous solvents) by vibrational circular dichroism spectroscopy for the first time. For comparative studies, vibrational absorption and electronic circular dichroism measurements were also carried out under identical conditions. The peptide was found to adopt β-sheet and β-turn structures, with their relative proportions changing in different environments.