Carpinus comprises approximately 35 species widely distributed from Europe to Eastern Asia, but relatively little systematic work has been done, apparently due to the difficulties of working with the greatest concentration of species in China. Thirteen flavonoids were isolated from the leaves of eight taxa, primarily, from Korea, representing one section (Distegocarpus) and three subsections (Carpinus, Monbeigianae, Polyneurae) of the other section (Carpinus) according to Kuang and Li`s classification. Flavonoids pattern in the genus was a simple one, based on the three common flavonols (myricetin, kaempferol and quercetin), and did not show apparent sectional differentiation among taxa considered. However, flavonoid chemistry was effective in the estimation of specific differentiation within each section or subsection. In section Distegocarpus, C japonica was discovered as a primitive taxa with myricetin compounds, and C. cordata var. chinensis as an advanced by the simplification of flavonoid compounds from C. cordata var. cordata. In the subsection Carpinus of section Carpinus, C. viminea var. viminea was discovered as primitive with myricetin, and C laxiflora and C viminea var. chiukiangensis as advanced by the gain of isoflavone, and by the simplification of flavonoid compounds respectively. Flavonoid chemistry also supported the treatment of subsects. Monbeigianae and Polyneurae as a unified group rather than as two different subsections. Considering morphological characters, flavonoid chemistry, and fossil evidence, it was evident that Carpinus should be treated as three different phylogenetic groups, section Distegocarpus, and subsections Carpinus and Monbeigianae (subsects. Monbeigianae+Polyneurae) of section Carpinus. After sections Distegocarpus and Carpinus had differentiated from Paeleocarpinus, subsections Carpinus and Monbeigianae differentiated later.