This paper aims to develop a GIS(Geographic Information System) application model as a decision-making support system in order to evaluate the potential of forests according to their functions, or to classify forest functions. The forest functions analyzed in this study are as follows: production of timber, stable supply of water resources, forest hazards prevention, recreation in forests, conservation of living conditions and natural environment. Using a model possible to evaluate the potential of each forest function and to assort forest functions by making priority-based decisions according to the functions, as well as allowing for various possible analysis environments, its application has been reviewed. Factors for assessing the forest functions could be built by using the following three categories: four maps-topographical map, vegetation map, forest site map and basic forest land use map-whose quantitative drawings had already been made; other self-established maps, such as one indicating the location of sawmills, location map of expressway interchanges, and spatial data of national population distribution map; and attribute data of population and precipitation. The GIS application developed here contributes to the evaluation of forest functions in all the subject areas by map units and national forest management districts based upon the assessment system.