Most Small Modular Reactors currently under development are pursuing designs that can demonstrate flexibility in terms of construction and operation, and seeking to adopt innovative technologies to implement them, which is a very big challenge not only from the developer’s perspective but also from the regulator’s perspective. For the successful development of SMRs, it is necessary to move away from the existing prescriptive regulatory approach and exercise regulatory flexibility to sufficiently reflect design characteristics. The reason why SMR development is actively progressing around the world is to overcome the limitations of existing Light Water Reactors. Licensing advanced reactors such as MSR, VHTR, and microreactors requires a different approach from the existing conservative regulatory framework, taking into account changing regulatory environment. With the development of information technology and artificial intelligence, new types of threats are emerging, most of which are related to nuclear security. The IAEA, as well as leading countries such as the United States and Canada, require that safety, security, and safety measures be reflected in the early stages of design (Safety, Security, Safeguards by Design) and should be applied in the regulatory process. In addition, it is recommended to design a system that can achieve synergy effects by identifying in potential issues that may cause regulatory interference between safety and security (SSI, Safety-Security Interface). The competitiveness of SMR in the international market will be highly dependent on the degree to reflect the importing countries’ requirements. Since most SMRs currently under development do not have significant differences in safety goals, multi-purpose usability, etc., it is necessary to faithfully reflect the environmental factors necessary for SMR operation in the adopting country in the design. The major issues expected are mostly nuclear security-related rather than safety, and the physical characteristics of the site including the geopolitical conditions of the importing country must be taken into consideration. In this paper, the necessity of SMR nuclear security regulation and the way how to reflect the Security by Design on SMR will be presented.