Ethylene is an unsaturated hydrocarbon that is released into the atmosphere of a mine as a result of an increase in the temperature of coal caused by the self-heating process. The content of ethylene in mine air is one of the indicators for assessing the degree of the coal self-heating process. Sorption capacities of hard coals with respect to ethylene may be the reason for the decrease in its concentration in mine air, which may affect the accuracy of self-heating process assessment. This phenomenon may be particularly important in the case of coals with significant sorption capacities. This paper presents the results of ethylene sorption studies carried out on six samples of bituminous coals collected from currently operational coal seams in Polish mines. The coals under analysis are characterized by varying sorption capacity with regard to ethylene. The highest sorption capacities were reported for low rank, high-porosity coals with easily accessible pore structure, high specific surface area values, and high oxygen content. The interactions between the electron-donor (and electron-acceptor) centers of coal surface and pi electrons of double bonds in gas-sorbed molecules are significant in the process of ethylene sorption. Coals with low oxygen content and more nonpolar surface structure, low porosity, and compact internal structures are characterized by low ethylene sorption capacity. On the basis of desorption studies, ethylene is a gas which once adsorbed mostly desorbs from coals. The percentage of desorbed gas increases with increasing temperature and it is higher for coals with high sorption capacities. Some of the undesorbed ethylene molecules remain in the coal structure. They are permanently bonded to the surface of coals, and their number depends on the type of coals and their sorption capacities.