Abstract Southeastern Guangxi is located in the southwestern South China Block and to the northwest of the South China Sea (SCS), with abundant records of the Cretaceous magmatism. A detailed study of igneous rocks will contribute to a better understanding of the late Mesozoic tectonic environment. Zircon U–Pb dating yields ages of 93.37 ± 0.43 Ma for Yulin andesites and 107.6 ± 1.2 Ma for Luchuan granites. Yulin andesites are hornblende andesites, of which w(MgO) is between 7.72% and 8.42%, and Mg# is between 66.7 and 68.0, belonging to high magnesian andesites (HMAs) from peridotite sources. Luchuan granites are medium- to fine-grained monzogranites. Monzogranites and clastoporphyritic lava are high-K calc-alkaline series and metaluminum to weakly peraluminous series, which belong to the I-type granites. Those are enriched in Rb, Th, K and LREEs and depleted in Nb, Ta, P and Eu, showing the geochemical characteristics related to subduction. Unlike the contemporary “bimodal igneous rock assemblages” in Zhejiang and Fujian, the intermediate-acid magmatites in the southeastern Guangxi imply the compressive tectonic environment. The assemblage of HMAs and adakitic rocks indicates that the southwestern South China Block was under the Neo-Tethyan subduction during Cretaceous, and slab melting contributed to the magma in this area.