During the last two decades, there has been a significant reduction in the number of banks in the Croatian banking sector. The aim of this paper is, through the calculation of various concentration indicators, to examine how the reduction in the number of banks affected the concentration of the banking sector. Using data on bank assets for 2005, 2010, 2015 and 2018, this paper analyzes the concentration of the banking sector in the Republic of Croatia using traditional market concentration indicators (concentration ratio and Herfindahl-Hirschman index) as well as six additional concentration indicators; Hall-Tideman index, Rosenblut index, Hannah-Kay index, U index, Hause index and entropy measures. The correlation matrix of the calculated concentration indicators indicates a high degree of correlation between, which leads to the conclusion that traditional concentration indicators are adequate for monitoring market concentration of the banking sector. Indicators focusing on banks with smaller market shares indicate a moderate degree of concentration, while indicators emphasizing banks with higher market shares indicate an oligopolistic market structure of the Croatian banking sector. Given that the market share of the four largest banks exceeds 60%, the latter conclusion nevertheless imposes itself as more correct.