Environmental impacts of various types of energy production are compared in the scope of an ongoing national research project “Life Cycle Assessment of Energy Production”. The project is using the LCA method to compare the potential environmental impacts of selected energy sources throughout their whole life cycle. The energy sources are representative for the energy grid of the Czech Republic. The inventory data used for the LCA are based on case studies of selected Czech power plants. Presented article is showing the preliminary results – the comparison of environmental impacts of two electricity sources. Lignite power plant and a hydroelectric power plant are compared. Only the impacts of plant operation are compared so far, the construction and decommissioning are not included in the current analysis.