The paper is the third part of the geographic essay on the area of Boka kotorska (the Bay of Kotor). In the first part, the authors (Crkvenčić, I.; Schaller, A., 2005) describes social and political changes in Boka kotorska and development of ethnic structure of the area until 1918. The subject of the second part of the essay(Crkvenčić, I.; Schaller, A., 2006) is ethnic structure of Boka kotorska in the period of Austrian rule (1814-1918). Finally, in this, third part, the changes of ethnic structure of Boka kotorska since the fall of Austrian regime onward are analysed. In the focus of the analysis is the phenomenon of a huge decrease of Croatian population in Boka kotorska. The explanation of ethnic development in the area begins with analysis of data obtained from the last Austrian census in 1910. There are two periods considered in the paper: (1) development of ethnic composition in the period of the Kingdom of Yugoslavia (1918-1941), and (2) ethnic features of the population of Boka kotorska in the period of federal Yugoslavia (1945-1991). In addition, the analysis of data by Montenegrin census in 2003 us made in the chapter titled «Croats in ethnic structure of Boka kotorska - the dying away of Croation population in Boka kotorska». [ABSTRACT FROM AUTHOR]