Abstract: Nuclear DNA C value and genome size are important characteristics of biodiversity. In this study, young leaves of 18 cultivars of ornamental crabapple (Malus spp.) were used as test material, and Zea mays L. cv. ‘B73’ was used as an internal reference sample. The genome size of ornamental crabapple was measured by flow cytometry. It provides a theoretical basis for germplasm resource identification, genomics research and new variety breeding of ornamental crabapple. The results showed that the C value of 18 samples of ornamental crabapple ranged from 0.74 to 1.50 pg, and the average size was 0.96 pg. Among them, ‘Mary Potter’ had the highest C value (1.50 pg), while ‘Red Jewel’ had the lowest C value (0.74 pg). ANOVA showed that there were significant differences in the C value between ornamental begonia cultivars. The research results indicate significant diversity in DNA C values and genome sizes among different ornamental crabapple cultivars.