The influence of ozonization of Kansk-Achinsk lignite on the chemical composition, structure and modified lignite reactivity in hydrogenation processes with different solvents (tetralin, coal derived liquid) and pyrite catalysts was studied. According to chemical analysis data the incorporation of oxygen into the organic matter of lignite takes place during ozonization, Some data indicating that ozonization results in loosening of the lignite structure were obtained by X-ray diffraction and e.p.r. techniques. Lignite modified by ozone treatment is more reactive, than untreated lignite, in hydrogenation reactions at 380 degrees C-430 degrees C in the presence of pyrite catalyst. For ozonized lignite the conversion degree was increased by 1.4 times in tetralin and 1.4-1.8 times in coal derived liquid in comparison with lignite previously treated in helium.