Change in demographic structure affects individuals and societies on a macro and micro scale and directs them to take precautions. When the subject is the future of social security, the importance of demographic structure in terms of sustainability increases even more. The term of sustainability, which is used along with many other concepts, has social, economic and environmental dimensions. The demographics of the world it is changing with increasing population, technological developments, economic conditions, security policies and especially immigration. Demographic changes in the globalizing world increase the future anxiety of individuals. Individuals struggle against the risks that occur in their lives such as birth, death, illness, disability, loss of job and income or increased expenses. For this reason, states, with the awareness of being a social state, establish social security systems so that individuals can continue their lives with their families in safety and plan their future lives in a healthy way. Since the states with strong financial structureshave advanced taxation systems and integrated sustainability policies, they can more easily meet the social security needs of their societies. The weak financial structures of developing countries and their unhealthy tax systems make it difficult to find solutions to demographic changes. This may threaten the sustainability of social security systems. There are different models in the history of the Turkish social security system. Comprehensive social security system was established in Turkey with the social insurance legislation that started in the middle of the 20th century and the scope was expanded with the protection laws that were enacted one after the other. The Turkish Social Security System basically consists of social insurance, social assistance and social services in a way that will serve the changes in the demographic structure. Having a population of approximately 85 million and an unemployment rate of 9.7% as of 2023, Turkey has hosted millions of foreigners admitted from different countries, both registered and unregistered, since 2011. The Turkish social security system is experiencing various problems due to the changes in the demographic structure with foreigners. Despite all the reforms, measures taken and state support since the 1990s, the deficit of the social security system is increasing exponentially. The additional burdens undertaken by foreigners make the sustainability of the social security system difficult. In this study, in which literature review and data analysis are made, the effect of the refugee, asylum seeker and immigrant population, which is increased with the entry of foreigners, especially Syrians, into the country, on the Turkish social security system is examined. Attention is drawn to the problems that may be encountered with the changing demographic structure and informal working conditions with foreigners and solutions are offered. In this context, it is necessary to take deterrent measures to register foreigners entering the country by making use of technological opportunities and to prevent their unregistered employment.

Keywords: Sustainability of Social Security, Demographic Structure, Social Security of Foreigners