The problem of methane existence in coal beds has been known for many years. It was and still it is a danger to coalminers. The aim of the research, presented in the paper, is to show and assess the porosity structure (especially micro and nanoporosity) in accordance to the dimensions of carbon dioxide particle. The characteristic surface morphology of the sample and the disclosure of the carbon porous structure have been obtained using the scanning electron microscope (SEM). The presented study of the coal microstructure is a part of the coal demethanation method with the use of liquid CO2, that has been proposed by the Military University of Technology.