Many countries have tried to make green building assessment systems, since the importance of sustainability in building industry has been recognized. As leaders of global green building assessment technologies, UK and USA have made their own green building assessment systems, named BREEAM and LEED. Korea has also made a proper building assessment system, named GBCS(Green Building Certification System) and started to implement the GBCS in 2002. BREEAM and LEED have been upgraded as the requirement of society for building industry has been changed. GBCS has also been upgraded and became effective in July 2010. The new system was improved, but still need to be looked carefully for a better performance. The goal of this research is to compare and analyze the three green building rating systems; GBCS, LEED and BREEAM. This study is focused on the suggestions for upgrading GBCS.