Due to its special situation, the Caspian region has been influenced by the political action of coastal and extra-regional actors. The geopolitics of this region and its effective foundations mutually give direction and meaning to the behaviour of the actors. The entanglement of three categories - geography, politics and power and the resulting forms of behaviour have created the question of what effect do the geopolitical foundations of the Caspian legal regime have on the national security of the Islamic Republic of Iran. In addition, the impact of geopolitical factors has consequences for the Islamic Republic of Iran which has brought about this research and which is also the search for truth. The following text is of a descriptive/analytical nature and a documentary/library foundation with the theoretical application of foundations and geo-political factors. The output of the research shows that geopolitics and its foundations, while creating the behavioural pattern of "opportunity" for the Islamic Republic of Iran, has provided the behavioural pattern of "insecurity" for this country. To be more precise, the geopolitics of the Caspian legal regime and its foundations, despite creating some opportunities for the Islamic Republic of Iran, the national security of this coastal player in the context of the geographical location and territorial space in the context of historical and civilizational developments, characteristics and the natural nature of the coastal area, territories and access to the sea and the territorial extent of the maritime country have been overshadowed and challenged.