Coal combustion in the power industry causes the emission of pollutants into the air and the production of a large amount of solid by-products, such as ash and slag. From the perspective of the circular economy, it is necessary to seek new applications for these types of materials in the industry. By recycling slag, the consumption of natural resources can be reduced, resulting in both economic and environmental savings. The objective of the article is a preliminary assessment of the dynamic properties of the combustion slag (CS) from “Siekierki” CHP Plant, Poland’s largest CHP plant, the second largest in Europe, located in Warsaw. To understand the dynamic properties of the CS, the resonant column tests were carried out. The paper presents the results of the dynamic shear modulus and damping ratio, the small-strain shear modulus and damping ratio, as well as the variation of these dynamic parameters with shearing strain. Both, the stiffness and damping properties of the CS have been conveniently correlated with the corresponding strain level (γ), mean effective stress (p’), and relative density (Dr). High similarity in dynamic shear resistance to natural non-cohesive soils may result in the future utilization of this material as a possible substitute for natural material in practical geotechnical engineering.