The Covid-19 pandemic has negatively affected social security systems already experiencing financial sustainability problems. In this study, the effect of the COVID-19 pandemic on the financial sustainability of the system was tried to be revealed with evidence-based data using a multi-criteria decision-making method. In the study, the social security system’s sustainability and annual performance levels were evaluated by technique for order preference by similarity (TOPSIS) method, which can be applied to different workplaces. In the study, 9 different criteria affecting the sustainability of the social security system were used. The data were obtained from the Social Security Institution Data Practice database. Data between 2014 and 2021 were included in the study. The findings of the study show that there is an increase in the invoice amount per application and the invoice amount per prescription in private hospitals, public secondary and tertiary hospitals, and university hospitals. The findings show that the Ci value closest to the ideal value is in 2015 (Ci2015=0,9318) and the farthest Ci value belongs in 2020 (Ci2020=0,1404). While the obtained Ci values were found to be within a certain range, it was determined that the pandemic in 2020 caused a major breakdown in the direction of the negative ideal. As a result, the sustainability of the social security system, which is currently experiencing problems, and the economic and social problems experienced globally with the pandemic have reached an even more important critical threshold for health politicians.