Mercury is known for primarily binding organically in lignite and inorganically in coal. The knowledge about the binding forms does not impact the speciation of mercury in the combustion chamber of a power plant. However, the relation between binding forms and release behavior is crucial for modelling the material flow of mercury in the firing process. Oxidizing agents like halogen salts could be added more effectively. There are different analyzing methods like the float-sink-analysis or the sequential leaching to determine the mercury binding forms. Nevertheless, there is no standard procedure for each analyzing method, which allows a comparison. In this work, mercury binding forms in Central German lignite were investigated. Results from thermal treatment of the lignite show a loss of mercury of 87% up to a temperature of 200 °C. The responsible mercury binding form for that release behavior is discussed by using the results of a leaching process for the extraction of humic substances, mercury analyses and simultaneous thermal analyses with mass spectrometry (TG/DSC-MS). The results show that mercury is bound to humic acids with 0.261 mg/kgdry and in humin with 0.735 mg/kgdry. The high mercury affinity of humic substances is noted as the result of chemical binding with functional groups like the carboxyl group, hydroxyl group and thiol group. Compared to the raw sample, a thermally treated lignite (at 200 °C) does not show any thiol group (m/z=48) in ion intensity measurement. This work proves the organic binding form of mercury with humic substances in lignite.