The information about genome size is implied in the studies of genetic diversity, the genome size evolution and can be used in breeding of new interesting cultivars. A total of 52 apricot cultivars, including 17 new perspective apricot hybrids planted in South Moravia region were analysed by flow cytometry. In addition, nuclear DNA content and ploidy level of 10 representative cultivars P. salicina, P. domestica, P. cerasifera and 22 interspecific hybrids of stone fruit were determined. Only the CV values lower than 5% were considered in analysis. All analysed apricot cultivars were diploid with average value of relative genome size 0.617 ± 0.014 pg/2C. The ploidy and DNA content of plums differ in botanical species. The obtained results were compared according to the geographical origin of cultivars and the theory about genome size evolution was considered. The values of relative genome size of original botanical species related to P. armeniaca (P. mume, P. sibirica, P. ansu) reached the lowest value in average compared with other cultivars in this study (0.603 pg/2C in average). Two pentaploids and one tetraploid were found in interspecific hybrids, which could be a part of interest of future studies.