Abstract:Onychium Kaulfuss, subfamily Pteridoideae of Pteridaceae, has long been in dispute with respect to its sectional circumscription and interspecific definition. We studied the phylogenetic relationships of Onychium based on five chloroplast DNA sequences(rbcL/atpA/matK/trnL-trnF/trnG-trnR) using Maximum Likelihood(ML) and Bayesian(BI) methods. (1)All species of Onychium were clearly divided into two main groups: Onychium japonicum(Thunberg) Kunze, O.tibeticum Ching & S.K.Wu, O.moupinense Ching, O.moupinense var. ipii(Ching) K. H. Shing, O.japonicum var. lucidum(D. Don) Christ, O.cryptogrammoides Christ and O.plumosum Ching were clustered in a group, while O.siliculosum(Desvaux) C. Christensen and O.tenuifrons Ching were clustered in another group; (2)It provided the molecular evidences for the taxonomy of Onychium at section level. O.japoniucm and O.japoniucm var. lucidum were not united together in the phylogenetic trees, while they were separated by other species, suggesting that O.japoniucm var. lucidum should be treated as a separate species rather than a variety of O.japonicum; (3)O.moupinense and O.moupinense var. ipii were gathered in a strongly supported clade, supporting the taxonomic treatment of O.moupinense var. ipii as a variety of O.moupinense in Flora of China; (4)O.tibeticum and O.japonicum were grouped in a clade with a high bootstrap value with close relation.