Abstract: A typical bimodal volcanic rock association, composed of basalt and rhyolitic volcanic rocks, is distributed in the Mesozoic Linjiang volcanic-sedimentary basin, which is located in the eastern segment of the Nanling tectono-magmatic belt and controlled by the Sannan-Xunwu fault belt. The Rb-Sr isochron ages of the basic end-member (basalt) and acid end-member (rhyolite) of the bimodal association in the Changpu Formation of the Yutian Group in the Linjiang area are 173.7 ± 2.5 Ma and 174 .9 ± 3.9 Ma respectively. Thus it is ascertained that the bimodal volcanic rock association is of Middle Jurassic age. This provides convincing isotope age evidence for the extension and break-up of the eastern segment of the Nanling during the Early Yanshanian.