The goal of this research is to show the political and geographical development of the Croatian Danube Region throughout the history as well as to contextualize causes and consequences of the change of the border which influenced the development of national sovereignty of Croatia. What is more, the emphasis is put on ethnic composition and on the contemporary Croatia-Serbia border dispute on the Danube river. The research was carried out through the analysis of the literature and cartographic representations alongside with the comparison of the demographic data after the change of the border’s role on Danube which serve as important evidence of how strong the political and geographical factors that had an influence on the border in Croatian Danube Region were. The results of this research show that the border in Croatian Danube Region was subjected to many political and geographical factors which moved the state line westward. Moreover, the Danube’s changed role as border since 1990 between Croatia and Serbia, encouraged by the Serbian aggression, had an influence on the ethnic composition on both sides of the river Danube. Furthermore, the International Court of Justice, which in its practice seeks to determine the border line on rivers, can encourage the two countries to settle their border dispute bilaterally.