The Ostracods studied in this paper were collected by the members of a geologicalparty in 1955 from the yellowish silt-clay in Gansen district,Chaidam Basin.Accord-ing to the collecter’s opinion,the geological age of the fossil bearing bed is Pliocene toQuaternary.The Ostracods are found in association with a charophyta,Chara gansenensis Wang(S.Wang,1961),gastropods and some indeterminable fragments of plant and fish bone.The species of Ostracoda described and illustrated in this paper are as follows:Ilyo-cypris gibba(Ramdohr),Eucypris inflata(Sars),Prionocypris gansenensis Huang(sp.nov.),Cypricercus brevis Huang(sp.nov.),Cypridopsis reticulata Huang(sp.nov.),Cyc-locypris serena(Koch),Candona neglecta Sars,C.houae Huang(sp.nov.),Limnocythere dubiosa Daday,L.sancti-patricii Brady et Robertson,L.binoda Huang(sp.nov.)and Cyprideis littoralis(Brady).From the geological distribution of this Ostracod assemblage,the fossil bearing bedmay be of Pleistocene in age.