Processes of transformation of economic system in Poland and accession to the European Union resulted in the changes in agrarian structure. Such changes were tended towards increase of level of economic activity of farms, however, other processes as decrease of number of farms and polarization of structure occurred in brighter extent. The aim of the study is to present changes in agrarian structure in Poland after accession to the European Union. Authors use statistical data, scientific and professional literature, reports of research institutes for the analysis. The analysis also is performed at regional level taking into account new definition of farm offered by the Central Statistical Office in Poland what provides new insight in the issue. Research results indicate that changes in agrarian structure differ across regions. In general, significant transformations in the structure of land use in Polish farms may be observed, particularly changes in scale of land use. The smallest farms were eliminated from economic environment, while medium-sized holdings became stronger. From the competitiveness standpoint, this change is beneficial. However, negative result may also be observed, i.e. increase in patchiness of fields what worsen spatial structure of lands. Results of the paper are based on the research tasks of the Jean Monnet Networks project No. 564651-EPP-1-2015-1-SK-EPPJMO-NETWORK “Sustainable Land Management Network”.