Evaluating environmental impacts of regional development projects has critical importance in environmental management aspect. This paper uses multi-attribute utility theory as a basis for obtaining a value index to assess the environmental impacts and applies the theory to a specific Korean case study. To structure and quantify basic values for the assessment, we elicited important attributes, then refined and structured them into a hierarchy. An environmental multi-attribute index is constructed as a multi-attribute utility function, based on value judgments provided by a group of technical experts, policy makers, and a decision-maker at Korean Ministry of Environment. The implications of the results are also discussed. We found that the work and results can provide valuable insights for assessment of environmental consequences.