LCA (Life Cycle Assessment) analysis for buildings became a part of G-SEED (Green Standard for Energy and Environmental Design), which is a certificate program for green building in South Korea, to provide additional credits for the certificate. In this research, LCA analysis of a specific building which fulfills G-SEED program is performed to verify the environmental impact during the entire life cycle of the building. Moreover, the results of the analysis are used to identify the period of building life cycle which provides environmental impact the most. As a result, practical solution to reduce environmental impact in architecture field is suggested.