This paper evaluates the implementation of ISO 9001 quality management systems (QMS) in local self-government institutions in the Republic of Serbia, with a focus on its effectiveness in enhancing operational performance and service delivery. The research draws on a diagnostic model provided in Annex A of the ISO 18091 standard, specifically tailored for local governments, to assess the level of compliance across 39 performance indicators. The study highlights the critical importance of organizational capacity in implementing QMS in local administrations, which often operate with fewer resources compared to regional and national public bodies. Although ISO 9001 certification is widely recognized, its real value lies in effective application. This research suggests that integrating ISO 9001 with other management systems, such as ISO 14001 for environmental management, can bring greater benefits. Additionally, the paper calls for further reforms and training in local self-government to improve the consistency and reliability of public service delivery.