This paper proposes an application of Geographic Information System (GIS) to distribution substation planning for distribution systems of Metropolitan Electricity Authority (MEA). The main objective is to serve future load growth and to increase the reliability of the distribution systems. GIS is extensively used in the planning process as it contains comprehensive topological information of electrical equipment from transmission substations, distribution substations, power transformers, and distribution transformers to revenue meters at customers' sites. It also gives the number of customers in each feeder and power demand in small areas. With this information, it is possible for MEA to have accurate and reliable results with effective investment. In addition, the system reliability in specified area can be evaluated.