Thermogravimetric analysis (TGA) of humic acid samples from low rank Anatolian (east of Turkey, Bingol) coal were investigated under atmospheric pressure. The samples were subjected for the decomposition of organic matter ambient to 800 degrees C at four different heating rates (5, 10, 15, and 20 degrees C min(-1)). The humic acid samples were started at decomposition between 170 - 206 degrees C and amount of residues varied 55-60% according to heating rate. Each of samples was showed a single step mass loss. TG/DTG data of samples were analyzed to determine activation energy values by Coats and Redfern method and Arrhenius method. Activation energy values are similar obtained from Coats and Redfern method and Arrhenius method and varied from 25 to 29 kJ mol(-1).