Expansionary monetary policy, combined with unconventional measures, led to a decline in the profitability of U.S. and European banks. In this paper, we study whether such measures also affected the asset concentration in the European banking sector. The findings of this research add value to previous research, taking a step deeper into examining the consequences of expansionary monetary policy. We find that reductions in the ECB?s key policy rate can predominantly explain the concentration growth in the Eurozone countries. The ECB?s monetary policy had a more substantial influence on the growth of the concentration of banks outside the Eurozone than the own monetary policies of those countries. In this way, expansionary monetary policy poses specific challenges to financial stability in Europe.