Supreme audit institutions (SAIs) are key independent institutions tasked with ensuring transparent and responsible management of public funds. The aim of this thesis is to compare SAIs in the Republic of Croatia and Spain regarding their organizational structure, legal framework, and the process of conducting state audits. In the Republic of Croatia, the role of the SAI is carried out by the State Audit Office (SAO), organized as a monocratic office without judicial powers. The SAO's responsibility includes conducting audits of financial reports of public entities, analyzing audit types performed, and providing recommendations for improvement. On the other hand, in Spain, the role of the SAI is entrusted to the Spanish Court of Auditors (SCA), structured as a court of accounts with judicial powers. In addition to conducting audits, the SCA deals with legal matters, allowing it to take legal actions to ensure the recovery of improperly spent public funds. Despite organizational differences, both SAIs conduct audits in accordance with International Standards and ethical codes, while also adhering to local laws. These audits encompass verification of the state, regional, and local public sectors, as well as political parties. Through an analysis of legislation, processes, and reports of each mentioned SAI, the thesis concludes that despite variations in organizational structure, SAIs in Croatia and Spain share the same purpose: ensuring transparency and accountability in the expenditure of public funds to enhance confidence in financial management and achieve a high level of integrity.