The IR spectra of cotton, PET, nylon 6, viscose rayon, polypropylene, acrylic, acetate rayon, and cotton/A fiber blend were obtained by using a FTIR spectrometric method. These all except cotton/A fiber blend spectra were weight-nomalized to a sample weight of 2mg with the scaling function in the arithmetic command. The IR spectrum of cotton/A fiber blend was digitally subtracted with the normalized A fiber spectrum until A fiber component was removed completely i.e. the difference spectrum resembled the spectrum of cotton. When this subtracting operation was carried out, the scale factor(FCR)A, which meant the content of A fiber in cotton/A fiber blend, was also determined. After that, the difference spectrum was digitally subtracted with the normalized cotton spectrum until cotton copmponent was removed completely i.e. one could obtain the zero spectrum having the flat base line throughout all wavenumbers. When the second subtracting procedure was carried out, the scale factor(FCR)C, which meant the content of cotton in cotton/A fiber blend, was determinded. The contents of cotton and A fiber were calculated from these two scale factors. These fiber contents by FTIR were very close to the real fiber contents.