After permanent shutdown, contamination existing in nuclear facilities must be removed according to decontamination and dismantling procedures to achieve the target end state. In Korea, Korea Research Reactor (KRR) Units 1, 2 are being decommissioned, and Kori Unit 1 is in the process of reviewing the final decommissioning plan for the start of decommissioning. In order to complete decommissioning of nuclear facilities, it is necessary to satisfy the dose criteria according to the residual radioactivity remaining in the site and buildings. In the United States, which has a lot of experience in decommissioning, Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) is used as a procedure for measuring and analyzing residual radioactivity. In MARSSIM, survey units are classified according to the level of contamination, and the radiation survey procedure and effort can be determined according to the survey unit level. After the radiological analysis and statistical verification of the survey unit, it is decided whether to release the site. At this time, the geographical area to be used as the background level is called the reference area. Therefore, selection of an appropriate reference area is important for accurate residual radioactivity analysis and for the release of the site. In this study, reference area evaluation cases and domestic decommissioning procedures were analyzed to derive considerations for selecting an appropriate reference area. For example, Zion NPP in the US selected a place outside the boundary of the restricted area unaffected by nuclear power plant operation as a reference area by referring to the meteorological monitoring report. Among Korea’s decommissioning procedures, the appropriateness of the reference area can be confirmed through the final status report submitted upon completion of decommissioning. However, since the selection and application of the reference area needs to be reflected during decommissioning, relevant information must be updated through periodic communication between operator and regulatory agency. The results of this study will be used as considerations for selecting a reference area.