Although assessing outdoor environment and green space in terms of sustainability and environmental performance is perceived as an important issue, most existing green building certification systems are more focused on buildings and indoor environment. Recently, the Sustainable Site Initiatives (SITES) has been developed by American Society of Landscape Architecture in order to evaluate sustainability of site development and outdoor environment. Separate from LEED, the SITES are increasingly receiving attentions as a reliable certification system in the United States. As a preliminary study to develop the items of outdoor environmental assessment, the present study is purposed to analyze the assessment items, grading system and applicability of SITES for better understanding on the system. Also it was compared to existing green building certification criteria, including G-SEED, LEED-NC, and LEED-ND in order to investigate similarities and discrepancies. The results would provide insights and basic data to improve assessment items for outdoor environment of G-SEED.