Series of cancer tissues and corresponding normal tissues of gastrointestinal tract (stomach, colon, esophagus) were studied by FTIR technique and the results showed the analogy of the spectra for the cancer tissues, while the spectra of normal tissues can be classified into three kinds. The secondary structures of protein were obtained by using deconvolution and curve-fitting techniques with Amide I bands and the results showed that the contents of alpha -helix and beta-sheet are different between the normal and cancer tissues.