Abstract Polymer blends are produced to achieve properties that pure polymers are unable to. The qualitative analysis of these blends is not always satisfactory to point out failures in the final product and, therefore, the determination of their content might be required. The aim of this study is to develop quantitative methodologies using Fourier transform infrared spectroscopy (FT-IR), reflection mode with the universal attenuated total reflectance accessory (UATR) and transmission techniques, for the determination of the content of each polymer present in the polymer blend poly (butylene terephthalate) (PBT) and polycarbonate (PC). FT-IR/UATR presented better results using the relative band (A1772/A1716). FT-IR/UATR presented error of 2.30%, which is a little higher than the accuracy limit of the spectrometer (≤2%), but still adequate for industrial applications.