The topic of this thesis is one of the fundamental principles of the Croatian law on general administrative procedure („Zakon o općem upravnom postupku“) - the principle of protecting the acquired rights of the parties. Firstly, in the thesis is analyzed the institute of legality (division, object, subjects, scope of action) and then concepts of „finality“ and „enforceability“, also it was pointed that there is significant difference between them. Through examples are clarified exceptional legal remedies which are regulated by the same law, also it was pointed on potentially problematic areas. The thesis explains in detail the principle of protecting the acquired rights of the parties as well as the principle of protection of the legitimate expectations of the parties because the two are inseparably connected to each other, although the latter is not explicitly prescribed by the Croatian law on general administrative procedure („Zakon o općem upravnom postupku“). An integral part of the thesis is also several interesting judgments, more precisely, sentences of domestic courts through which the theme of the thesis was intended to be conveyed. The final part of the thesis refers to the analysis of decisions of the city assembly of the city of Zagreba (Gradska skupština Grada Zagreba) on the abolition of the parent-educator measure. At the very end of the thesis, everything important regarding the topic of the thesis is briefly summarized and a list of literature is provided.