Abstract: The basalts of the Changpu Formation of the Yutian Group in the Longnan-Xunwu area of Southern Jianxi were formed in the Middle Jurassic Epoch with a Rb-Sr isochron age of 173-176 Ma，and are the basic endmenber of the bimodal volcanic rock assosiation．The Pb-Nd-Sr isotope compositions of basalts are as follows：enriched in radiogenic lead，(206Pb／204Pb)i= 17．872～18．653，(207Pb／204Pb)i=15.434 ～16.131，(208Pb／204Pb)i=37．837 ～39．194；intermediate initial Nd isotopic ratios，εNd(t)= -0.4+1.1；and distinctive high initial Sr isotopic ratios，ISr=0．70835～0．71115．On the Pb-Pb diagrams．the basalts are plotted above NHRL line and have obvious Dural anomaly：Δ7／4Pb=0．19～61．7(22．1 in average)；△8／4Pb=59．2～101．5(71．03 in averag)；ΔSr=80～111．5(91．5 in average)．The Sr-Nd，Sr-Pb，Nd-Pb，Pb-Pb relationships of basalts strongly suggest a mixing source of the depleted mid．ocean ridge basalt mantle endmenber(DMM)and with the EM II enriched mantle endmenber．According to double-variation and two-component(Sr-Nd)mixing equation，calculation shows that the depleted mantle endmember and the EMII enriched mantle endmember for rock-forming materials of southern Jiangxi basalts are 58％ 一64％ and 42％ 一36％ ．respectively．The E-W trending Middle Jurassic bimodal volcanic rock belt in East Nanling area implies a major extensional tectonic event during the Early Yianshanian period．On the basis of Sr-Nd-Pb isotope geochemical and tectonic features mentioned above，it is assumed that the endmember component of EM II of Mesozoic mantle souses in southern Jiangxi was derived from the Gondwanaland．