The depletion of the conventional energy sources, as well as the degradation and pollution of the environment by the exploitation of fossil fuels caused the development of renewable energy sources (RES), including biomass. In Poland, biomass is the most popular renewable energy source, which is closely related to the obligations associated with the membership in the EU. Biomass is the oldest renewable energy source, and its potential, diversity and polymorphism place it over other sources. Besides, the improvement in its parameters, including an increase in its calorific value, resulted in increasing use of biomass as energy source. In the electric power industry biomass is applied in the process of co-combustion with coal. This process may contribute, inter alia, to the reduction in the emissions of carbon, nitrogen and sulfur oxides. The article presents the characteristics of the biomass burned in power boilers of one of the largest Polish power plants, located in Opole Province (Southern Poland). Besides, the impact of biomass on the installation of co-combustion, as well as the advantages and disadvantages of the co-combustion process not only in technological, but also environmental, economic and social aspects were described.