The most important Colombian coals were studied using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) Spectroscopy. The ATR-FTIR spectra were used to obtain structural parameters of coal and correlating these structural parameters with the rank of the coal. The structural parameters, methylene-methyl ratio (CH 2 /CH 3 ), aromaticity factor (f a ), aliphatic-aromatic ratio (H al /H ar ) were determined directly from the ATR-FTIR spectra and f a was evaluated from spectra data and an elemental analysis in coals studied here. The aliphatic and aromatic regions were considered between 3000 - 2800 cm -1 and 912 - 670 cm -1 , respectively.