There has been a significant decrease in genetic diversity on a global scale for several livestock species, including beef cattle. Therefore, the aim of this study was to deliver fine-scale analysis of the genomic structure and to describe the diversity status of six beef cattle breeds, with a specific focus on genomic inbreeding and the trend of effective population size. The genomewide data of 639 animals belonging to cosmopolitan (Aberdeen Angus, Charolais, Hereford and Limousin) and local (Piedmontese and Romagnola) cattle breeds were included due to their importance for the local and global beef industry in Europe. In addition, the local dual-purpose Slovak Pinzgau was used to extend the study due to increasing interest from beef cattle breeders in Slovakia. The results showed that more than 3% of the Aberdeen Angus, Hereford and Romagnola genomes, less than 1% of the Limousin, Charolais and Slovak Pinzgau genomes and 0.38% of the Piedmontese genome could have been significantly affected by the mating of relatives over the last three generations. The estimates of effective population size indicated a linear decline within each of the analysed populations. The decrease was mainly evident in populations of the Slovak Pinzgau (7.39 animals per generation), Limousin, Piedmontese and Charolais cattle (average 5 animals per generation). Due to the fact that the decrease in effective population size may be accompanied by a decrease in breed competitiveness with regard to a changing production environment, genetic diversity should be continuously monitored to preserve the long-term potential of the analysed breeds.