<p>Given a heavy dependence on imported fossil fuel for its primary energy supply, Japan must address the pressing issue of curtailing its carbon emissions whilst enhancing its energy security. Hydrogen technology could provide a potential solution and has received great attention by the Japanese Government where they strategise a large-scale hydrogen supply system from 2030 that will inevitably affect the energy security situation of Japan. A closer examination of the potential effects is therefore imperative as the security of stable energy supply directly influences the stability of the economy. This research therefore, aims to assess how the diffusion of hydrogen, given various hydrogen supply chain scenarios, may affect Japan's energy security through the construction of an energy security index.</p>