The theory of the constitution in the material sense has occupied the attention of theorists of many disciplines for almost two hundred years. Because of its polemical nature and difficult determination of what a material constitution is in general, this theory was also considered somewhat controversial, even undesirable for constitutional theory. This thesis, following the trend of European constitutional theory of the last 10 years, which has again become more active in studying this "dangerous" topic, seeks to explore whether the concept of material constitution has any epistemological value for theoretical and practical considerations of constitutional law. Guided by the theoretical principles of Marco Goldoni, as one of the main leaders of the new wave of interest in the material constitution, this thesis applies the "material study of constitutionalism" on the Republic of Croatia. In an effort to be a corrective to formal constitutionalism, the inclusion of the material level in constitutional considerations seeks to contribute to further deepening and better explaining the constitutional reality, and in particular the idea of how to understand constitutional change. Given that constitutional change is a very broad concept, this thesis focuses on the doctrine of “unconstitutional constitutional amendments”, which leaves behind numerous and still unresolved issues. The first part, as an introduction to the issue, presents the genesis of this doctrine in the Croatian constitutional order through the 2013 decision of the Constitutional Court regarding the referendum on the constitutional definition of marriage. In this part, in addition to the chronological presentation, the Croatian case from 2013 is placed within the broader theoretical framework of the doctrine of "unconstitutional constitutional amendments". In the second part, attention is focused on the material constitution as understood by Marco Goldoni, with a broader historical account of different ways of understanding the constitution in the material sense to more easily express the sources from which Goldoni built his own understanding. The third part of the paper seeks to give a material view of the constitutional changes to the Constitution of the Republic of Croatia, as well as to show what and to what extent is the epistemological value of the constitution in the material sense.