This presentation introduces application cases of open source GIS for scientific national park management in Korea. Korea National Park Service (KNPS) is a public organization that manages almost all domestic national parks. GIS is a core technology for the park management, but the cost of commercial software had been limited the diffusion of GIS. Now, park rangers of KNPS are using QGIS that is a representative open source geospatial software, and they make themselves various GIS and remote sensing-based maps. For this, KNPS launched a QGIS education program for employee training. As a result, they started making maps using QGIS and many useful plugins, including Animove for QGIS, Semi-Automatic Classification Plugin (SCP), and Oceancolor Data Downloader. A variety of natural resources maps can be made from GPS field data, and time-series satellite images can be processed into climate change effect maps such as forest health, sea surface temperature (SST). Moreover, a graphical modeler feature of QGIS enables an automatic data processing. The Drone Flight Simulator called Park Air System, is also being developed using open source geospatial libraries. Using QGIS, KNPS makes all geospatial data like a trail, facility, and natural resources and is opening to the public freely. KNPS won the President's Prize in 2014 for the hard work.