Volcano-sedimentary series of the Upper Jurassic to the Lower Cretaceous are extensivelydeveloped in Zhejiang Province.But ages and stratigraphic correlation concern-ing these rocks have long been a controversial problem.Systematic samplingwas made of volcanic rocks of the Laocun,Huangjian,Shouchang and Moshi-shun Formations in western Zhejiang considered thus far as the Late Jurassic.Isotopicage determinations show that U-Th-Pb zircon ages are approximately concordant with Rb-Srisochron ages,whereas K-Ar biotite ages and K-Ar isochron ages are all slightly lower.Itcan therefore be established that the ages of volcanic rocks mentioned above range from134±6 to 122±2 m.y.,corresponding to the“transitional period”from Jurassic to Cretaceous.It can also be concluded that the rocks have not undergone apparent epigenetic metamor-phism.The initial ~(87)Sr/~(86)Sr ratio is about 0.7089—0.7121,on the basis of which it may bepostulated that the volcanic magma seems to have originated from the upper mantle withcontamination by sialie materials subsequent to differentiation.For age determinations of such acid volcanic rocks Rb-Sr isochron method is consideredmore suitable in view of its following advantages:the high reliability of results;wide appli-cability to different samples;smaller sample requirement and the possibility for furtherstudies involving petrogenesis by use of initial ~(87)Sr/~(86)Sr ratio. Volcano-sedimentary series of the Upper Jurassic to the Lower Cretaceous are extensivelydeveloped in Zhejiang Province.But ages and stratigraphic correlation concern-ing these rocks have long been a controversial problem.Systematic samplingwas made of volcanic rocks of the Laocun, Huangjian, Shouchang and Moshi -shun Formations in western Zhejiang considered thus far as the Late Jurassic. Isotopicage determinations show that U-Th-Pb zircon ages are concordant with Rb-Srisochron ages, K-Ar biotite ages and K-Ar isochron ages are all slightly lower .Itcan therefore be established that the ages of volcanic rocks mentioned above range from 134 ± 6 to 122 ± 2 my, corresponding to the “transitional period” from Jurassic to Cretaceous. It can also be concluded that the rocks have not undergone apparent epigenetic metamor- phism.The initial ~ (87) Sr / ~ (86) Sr ratio is about 0.7089 ~ 0.7121, on the basis of which it may bepostulated that the volcanic magma seems to have originated fro m the upper mantle withcontamination by sialie materials subsequent to differentiation. For age determinations of such acid volcanic rocks Rb-Sr isochron method is consideredmore suitable in view of its following advantages: the high reliability of results; wide appli-cability to different samples; smaller sample requirement and the possibility for furtherstudies involving petrogenesis by use of initial ~ (87) Sr / ~ (86) Sr ratio.