This study analyses the aged population and its impact toward Japan national security. Japan faces a rapidly aging population, a demographic shift that has profound implications for national security. This study also shows the challenges posed by this trend, focusing on its effects on economic stability and social cohesion. This study has three objectives. First, to identify the factors of Japan aging population. Second, to examine the impact of Japan aging population towards Japan's National Security. Third, to analyse the strategy of Japan towards aging population. The conceptual underpinning of this study is national security. By using a qualitative approach, secondary data was collected from reliable printed and online documents. The findings of this study are that, first, low birth rates, high life expectancy, and socio-economic factors such as urbanization and changing family structures as primary contributors to the aging population. These factors have led to a shrinking workforce, increased healthcare costs, and a growing dependency ratio, challenging Japan's economic sustainability and societal cohesion. Secondly, the aging population directly affects Japan’s national security by reducing the workforce, less childbirth, rural depopulation and elder care. This study concludes that despite the challenges, Japan has implemented several strategies, including policies to encourage higher birth rates, initiatives to extend the retirement age, and measures to increase the participation of women and older adults in the workforce. Furthermore, Japan has cautiously embraced immigration reform to address labour shortages and invested in automation and AI technologies to offset workforce declines. This study underscores the need for a multifaceted and adaptive approach to ensure that Japan can navigate the complex interplay between demographic trends and national security effectively.