Abstract: In order to quantitative analysis fiber content by FTIR, the infrared absorption spectra of polyester, cotton and polyester/cotton blends were measured, and the method for quantitative determination on blend ratio of polyester/cotton by FTIR was discussed. The results show that the linear relationship between the absorption peak areas of 2900 cm-1, 1717 cm-1, 721 cm-1 and polyester content in the polyester/cotton blends are not very clear. Six characteristic parameters are constructed from the three absorption peak areas, four of which have good linear relationship with the polyester content. Further demonstration tests show that the linear relationship between the sixth characteristic parameters and the polyester content is the best, and the derived linear equation can be used to determine the polyester/cotton blend ratio.