The paper aims to present basic types and reasons of the economy of scale advantages in the banking sector. Such advantages might be achieved thanks to a company´s growth (internal advantages) or an industry development (external advantages). In order to influence the banking sector´s structure it is extremely important to study related advantages of the economy of scale. Occurrence of such advantages should lead to the reduction of banking institutions´ number and increase of their size. On the other hand, however, one should also consider an excessive concentration in the banking sector.