The environmental aspects of the electricity supply system in Korea has been analyzed from the point of view of Life Cycle Assessment (LCA). As an initial step, thermal power generation, which has the largest portion in national electricity system and is considered to release significant amounts of emissions, is defined as the system. All the inputs and outputs associated with the defined system has been identified and calculated based on the delivery of 1kWh electricity generated by thermal power to consumers. The national electricity supply system is a circle-network type connecting the whole country to a single super grid with all generators feeding into it and all consumers drawing from it. Thus, the national averaged data have been collected and used to describe the present system. The Life Cycle Inventory Analysis (LCI) results show that anthracite releases the largest amount of airborne emissions and LNG releases the smallest amount of emissions among the fuels used in thermal power generation. The most dominant airborne emissions is CO₂ which is one of the main causes for global warming effect. Waterborne emissions like COD, SS, oil etc and solid wastes such as waste synthetic resins and combustion ashes are also quantified. The results of the analysis carried out here will be a part of the basic database for indispensible electricity in LCA studies for almost all industries.