Abstract: By screening different combinations of dissociation solutions and internal standards, the DNA C-values of six polyploid plants of subgen. Yulania (Magnoliaceae) were determined and analyzed by flow cytometry. Results showed that, in the screening of solution buffers and standard samples, woody plant buffer (WPB) was the best choice for subgen. Yulania. Furthermore, the peak pattern of mixed samples worked best when Magnolia stellata (Siebold & Zucc.) Maxim. was the internal standard and the coefficient of variation (CV) of the DNA peak was less than 5.0%. The C-values of M. liliiflora Desr., M. polytepala Law, R. Z. Zhou & R. J. Zhang, M. cylindrica E. H. Wilson, M. denudata Desr., M.×soulangeana Soul.-Bod., and M. acuminata (L.) L ranged from (3.92 ±0.02) pg to (5.85 ±0.03) pg and the genome size ranged from (3832.13 ±24.67) Mbp to (5964.17 ±56.06) Mbp. Thus, our results showed that the optimized flow cytometry system accurately determined the DNA C-value of polyploid species in the subgen. Yulania.