This paper presents site survey processes and the results for installing GBAS Category-I ground system into Gimpo international airport. For siting assessment, many things should be taken into account in advance, such as installation requirement of GBAS components, future airport development plan and possible interference effects to existing facilities. Because overall performance of GBAS system can be affected by GPS signal reception environment, on-site survey should be performed carefully to measure actual GPS environmental performance and determine if any adverse multipath or RFI problems exist or not. In addtion, VDB antenna should be located to ensure line of sight for transmitting VHF signal to deliver GBAS message to aircraft. Based on the survey results, final location for GBAS system installation is selected near runway 32 in the Gimpo airport.