The original and deconvoluted spectra of Attenuated Total Reflection (ATR) FTIR have been determined for both benign and malignant tumor tissues samples and the spectral differences have been investigated between the two types of samples. In comparison with the benign samples, the characteristic changes of malignant ones mainly involve: The prominent bands 1652 and 1645cm-1 due to the proteins in the α-helical and the unordered-random-coils substructures become stronger compared to those in the β-sheet and the turns substructures, suggesting that the former type of proteins increase in content in contrast to the later. The phospodiester band 1083 cm-1 of the nucleic acids becomes strongest on cancer tissues spectra and its area ratio to the amide II band 1548cm-1 rises greatly, indicating that the DNA content rises remarkably. The collagen proteins reduce in content while phosphorylated ones rise, and some hydrogen bonding is nearly broken in amino acid residue C-O (H) groups. The glycogen content decreases, and the CH2 content is higher than CH3 one. These results suggest that ATR-FTIR spectroscopy has the potential to become a powerful tool for biochemical studies and in vivo diagnosis of human breast cancers.