Abstract: 【Objective】Acer plants have potential value as ornamental plants and as a source of medicinal compounds. However, their use is hindered by a lack of molecular biology and genomic data. Presently, flow cytometry was used to examine Acer palmatum Thunb. and A. truncatum Bunge genome sizes, to provide foundational data for cytogenetics and genomics studies of Acer Linn.【Method】Fresh leaves of A. palmatum Thunb and A. truncatum were collected. LB01 and PI were used as isolation buffer. Zea mays L. CE-777 was used as the internal standard for the flow cytometry analyses. 【Result】Samples and the internal standard were better dissociated by the LB01 solution, with particles clearly distinguished and concentrated without overlapping peaks. The genome size of A. palmatum and A. truncatum was 0.840 4 and 0.756 0 pg, respectively.【Conclusion】Optimized sample processing and flow cytometry permitted the determinations of the genome sizes of A. palmatum Thunb and A. truncatum Bunge. The optimized processing and results enrich the Acer gene database and provide foundational data for investigations of origin and evolution of species, and genome sequencing.