Vegetation Index(VI) derived from remote sensing data is used to assess ecosystem factor in Environmental Impact Assessment(EIA) process. Ecosystem factor has been prepared by Degree of Green Naturality(DGN) mainly in Environmental Impact Statements. But DGN has room for improvement of assessing actual ecosystem situation. The objectives of this study are to define the relationship between field measure DGN and VI, and to develop methodologies to use VI for assessing the status and conditions of natural ecosystem. For verification of DGN and VI, 35 sites using global positioning system are selected and reviewed. Correlation coefficients of DGN and VI shows highly as 0.69. Also VI in EIA found it can be applied to assess ecosystem. It concluded that VI as well as DGN can be applied to assess ecosystem newly and largescale.