The issue of accountability is extremely important due to the efforts to measure the degree of efficiency of political systems. Recently, the researches on accountability are conducted at the supranational level, including research on the European Union system. Therefore, this article will try to answer the question whether or not the mechanisms of accountability promote efficient governance in transnational dimension in the European Union and also whether these are just another carbon copy of the solutions adopted in national States, which are not applicable at transnational level. Consequently, we will investigate the functioning of the key institutions and bodies of the European Union in terms of accountability. To examine how efficient is the system of accountability in the European Union in terms of multi-level governance we will be using model of accountability proposed by Guillermo O’Donnell.