Firing of bricks is essential manufacturing process during which the bricks obtain all the necessary properties. Life cycle assessment studies show that this process is also the most energy intensive of the brick manufacturing processes and results in the largest environmental impact. Usually kilns are fired with natural gas, therefore substitution of fossil fuel with renewable energy source is considered as one of the most effective approaches for reduction of environmental impact. Bio-synthetic natural gas (bio-SNG) is one of the most feasible substitutes of natural gas and therefore the aim of the study was to compare environmental impacts of those energy sources. Comparison of life cycle environmental impact of natural gas and bio-SNG was carried out using GEMIS (Global Emission Model for Integrated Systems) database. Both energy sources were compared on the basis of life cycle CO2 emissions, cumulated energy and material requirement, land use and employment effects. Results show that by replacing natural gas with bio-SNG greenhouse gases could be reduced and employment increased. However, cumulated energy, material and land requirement is larger when bio-SNG is used instead of natural gas.