The Xiankou ring complex in Le’an county, Jiangxi province is mainly composed of the huge-grained phenocysts-bearing biotite monzonitic granite externally and small-grained phenocysts-bearing biotite monzonitic granite internally, which is penetrated by the fine-grained alaskite dykes. LA-ICP-MS U-Pb zircon ages are obtained for huge-grained phenocysts-bearing, small-grained phenocysts-bearing biotite monzonitic granite and alaskite with weighted ages of 230±4Ma, 235±3Ma and 235±3Ma respectively, All the rocks are characterized by relatively high silicon (SiO2=70.35%~76.89%), alkali (Na2O+K20=6.77%~11.40%) and the weak to strong peraluminium values (A/CNK=1.00~1.18, an average of 1.07). The plutons have high concentrations of rare earth elements \[??REE=(121.52~383.33)×10-6\] and high field strength elements (Y, Zr, Nb, etc.), but the later dikes own low REE \[??REE=(25.85~43.75)×10-6\] values. The rocks are characterized by genesis type between S-type and aluminous A-type granite. (87Sr/86Sr)i=0.7082~0.7120,εNd(t)=-7.07~-8.10, mean value is -7.48, t2DM=1585-1669Ma, and mean value is 1618Ma. It suggest that the magma sources are mainly composed of old crustal rocks and involve some portions of mantle materials. The lead-isotope evolution for K-feldspar also indicate that are mixed mantle-crustal derived. we propose that the Xiankou granitoid produced in post-orogenic tectonic setting.