Biomass is commonly considered as a renewable fuel, which taking into account emission of CO2 does not contribute to the emission of the greenhouse gases. In the research, combustion tests of two types of fuel formed on the basis of straw with addition of polyethylene were performed in the laboratory. The article presents results of measurements of gas pollution coming from the combustion of the formed fuel. Obtained results were compared with similar literature data for the combustion of coal. The research covers also testing of chemical content, content of heavy metals and selected physical properties of ashes generated during the process of burning fuel based on straw.