Abstract:Total DNA from 54 individual plants collected in 27 sample sites of 10 Oxytropis species in Inner Mongolia was extracted in this research,and the trnL-F sequence was amplied and sequenced.Then the sequences were analyzed by ClustalX and MEGA 5.0.The phylogenetic tree was constructed by Maximum Likelihood methods in MEGA 5.0.The results showed as follows:(1)In the 10 Oxytropis species,there were 54 variable sites,46 informative sites and 1.9% of the inter-specific difference,and the GC contents of the trnL-F region were between 30.69%~31.50%.(2)The Oxytropis sp.were monophyletic,clearly separating from the Astragalus sp..The bootstrap value was 99%.(3)The samples of Oxytropis glabra itself clustered a group which was relatively evolved independently.The samples of O.verticillaris,O.racemosa and O.ochrantha mixed.Therefore they showed a close relationship.We are congruent with the points in Flora of Intromongolica,which consensus putting the three species into Subgen.Euoxytropis Sect.Baicalia Stell.ex Bunge.(4)Different samples of O.aciphylla were divided into two major branches,and the taxonomic position of O.aciphylla at subgenus level needs further investigation.(5)The samples of O.ciliata and O.inschanica clustered a group,which also supported the consensus which put them into Sect.Xerobia Bunge.The investigation results indicated that trnL-F sequences provided the molecular evidences for the study of the phylogenetic relationships in the Oxytropis at subgenus,sects and species levels.