Fiscal sustainability is crucial for the overall economic security of a country. It means the ability of the government to meet its financial obligations in the long run without relying on excessive borrowing and without resorting to inflationary policies. The purpose is to explore the key challenges to strengthening fiscal sustainability as an element of national economic security in the face of new geopolitical risks. Global economic crises, such as the 2008 financial crisis, the coronavirus pandemic, the war in Ukraine, crisis events in the banking sector in March 2023 can also affect fiscal sustainability. Economic crises can lead to a decline in demand for goods and services, lower tax revenues, and increased government spending on social programs such as unemployment benefits. This can lead to an increase in public debt and budget deficits. High levels of public debt also increase the risk that the government will default on its obligations, which could undermine investor confidence and increase borrowing costs. This can further exacerbate the problem of high public debt, as the government may have to devote even more resources to servicing this debt. According to the concept of "debt rejection" for developing countries, as a rule, there is a "lack of freedom" regarding the regulation of the debt level, although it is managed using the most modern methods. Identifying the determining factors for a specific country, highlighting the threshold of "rejection" of debt is a basic approach to debt management, in particular, its restructuring, determining an acceptable level of debt, using international lending to mitigate fiscal shocks and accelerate growth. To address the problem of high public debt, governments can implement measures such as spending cuts, raising revenues through taxation, or implementing structural reforms to improve economic growth. However, these measures can be difficult to implement as they may require difficult choices and sacrifices. Nevertheless, addressing high public debt is important for achieving fiscal sustainability and promoting national economic security.