Major and trace elements, REE concentrations and Sr, Nd isotope composihons have been measured in Bianmgou basaltic andesite-rhyolite bimodal association of intraoceanic arc of early Paleozoic age. Basaltic andesites have high MgO (5.78~9.71%) and very low TiO2, (0.30~0.45%) content with Ti/Zr ratios 63~73. Their REE show flat or slightly LREE depleted patterns with (La/Yb)= 0.65~1.55 and the HREE concentrations are relatively low with YbN ranging from 5~9. They are also depleted in HFSE (Zr,Nb, Y, V) with some 8~10 times the Zr chondritic abundances and 5~9 times of the Y chondritic abundances. All of these give them a strong affinity with boninite. Rhyolites are characterized by very low but rather constant contents of TiO2, and incompatible trace elements like La, Th, Nb or Zr, and show flat or slightly enriched LREE patterns with (La/YbN)ranging from 1~3 and with 11~37 times the La chondritic abundances and a negative Eu anomaly. They exhibit a pronounced Nb and Ti giving them a strong affinity with island arc series. The εNd (t) values of rhyolites and basaltic andesites fall in the range of +3.5 to +3.9 and of+3. 1 to +3.4. Basaltic andesites are likely to be evolved from partial melting of mantle wedge. Inconstant trace element ratios throughout the association and dominant rhyolites in the association rules out the fractionation-controlled origin of rhyolitic magmas, but support the hypothesis that Bianmagou rhyoIites may be formed by anatexis of hydrothermally altered local oceanic crust.Bianmagou bimodal volcanic rocks record a magmatism of inter-arc basin environment Major and trace elements, RE isotopic and Sr, Nd isotope composites have been measured in Bianmgou basaltic andesite-rhyolite bimodal association of intraoceanic arc of early Paleozoic age. Basaltic andesites have high MgO (5.78-9.71%) and very low TiO2, (0.30 ~ 0.45%) content with Ti / Zr ratios 63-73. Their REE show flat or slightly LREE depleted patterns with (La / Yb) = 0.65 ~ 1.55 and the HREE concentrations are relatively low with YbN ranging from 5 ~ 9. Also of depletion in HFSE (Zr, Nb, Y, V) with some 8 to 10 times the Zr chondritic abundances and 5 ~ 9 times of the Y chondritic abundances. All of these give them a strong affinity with boninite. Rhyolites are characterized by very Low but rather constant contents of TiO2, and incompatible trace elements like La, Th, Nb or Zr, and show flat or slightly enriched LREE patterns with (La / YbN) ranging from 1 to 3 and with 11 to 37 times the La chondritic benefits and a negative Eu anomaly. They exhibit a pronounced Nb and Ti giving them a st The εNd (t) values ​​of rhyolites and basaltic andesites fall in the range of +3.5 to +3.9 and of + 3. 1 to +3.4. Basaltic andesites are likely to be evolved from partial melting of mantle wedge. Inconstant trace element ratios throughout the association and dominant rhyolites in the association rules out the fractionation-controlled origin of rhyolitic magmas, but support the hypothesis that Bianmagou rhyoIites may be formed by anatexis of hydrothermally altered local oceanic crust.Bianmagou bimodal volcanic rocks record a magmatism of inter-arc basin environment