The Yongan granitoid pluton, which is located in the southern Qinhang suture zone, is a part of the Darongshan-Shiwadashan composite pluton in southeastern Guangxi. The pluton is composed of porphyritic cordierite-biotite granodiorite. The results of zircon U-Pb dating indicate that the age of the Yongan pluton is 252.8±3.3 Ma, suggesting Late Permian granites. The geochemical characteristics of the granites of Yongan pluton show that the rocks are rich in Al, K. A/CNK ratios are higher than 1.1. The standard mineral corundum molecules are more than 1%. In addition, the rocks are enriched in LREE, and depleted in HREE, and exhibit obvious fractionation between LREE and HREE. The chondrite-normalized REE patterns show right declining, exhibiting enrichment of LREE and slightly negative Eu anomalies. The granites are enriched in large ion lithophile elements (Rb, Ba, K, Sr) and depleted in high-field strength elements (Nb, P, Ti,Ta) and Ba, Sr. Zircon Hf isotopic compositions of the porphyritic cordierite-biotite granodiorite are mainly characterized by εHf(t) values of -14~-8, and the two-stage model ages of 2.3 to 1.8 Ga. In combination with previous data and an analysis of mineralogy and geochemistry as well as the zircon Hf isotopes and trace elements, it could be concluded that the Yongan pluton is strongly peraluminous S-type granite derived from the crustal source. Though the mantle failed to provide the rock material, the heat for the formation of magma was probably provided by the mantle underplating. The granite was formed in an extensional environment of the post-collision stage.