In recent years, financial sustainability (FS) of public policies has become a key concept in all governmental levels due to the need for ensuring public services delivery for future generations. Prior research has been focused on the financial sustainability in local governments (LGs) although its findings suggested the need to analyze this magnitude in other levels of government because political decisions could be different in each type of public entity. So, FS has also become very relevant in the Regional Government (RGs) context because their public policies affect not only at the regional level but also the local one. Therefore, from a comparative approach, this paper seeks to identify socio-demographic factors which could influence on the financial sustainability, in the Spanish context for both LGs vs. RGS in order to establish public policies to make sustainable public goods and services. Findings demonstrate that differences in influential factors between these two levels of public administration exist: factors such as population size and foreign population could have an effect on the financial sustainability of both governmental levels while the unemployment rate, dependent population, and population density affect differently on LGs and RGs.