Objectives: Southeast Yunnan is located on the southwestern margin of the Youjiang Basin. There are many controversies regarding the tectonic evolution of the Late Paleozoic. Whether there are relics of ocean basins in the Southeast Yunnan - border area of Yunnan and Guangxi between the Yangtze Block and the Cathaysian Block from the Paleozoic to the Triassic, or whether it was merely a rift environment, is one of the important issues in the study of the evolutionary history of the South China Plate. Results:Through 1:50,000 field geological surveys, a set of marine basic volcanic rocks intercalated with intermediate-acidic volcanic rocks and radiolarian cherts has been identified in the Huajia area of Funing. The volcanic rocks develop pillow structures and spherulitic structures, forming a typical marine volcanic rock assemblage. Zircon U-Pb dating of the dense basalt yields an age of 260.3±2.4 Ma (n=9, MSWD=0.34), indicating that the volcanic rocks formed in the Late Permian. Geochemical characteristics show that the volcanic rocks belong to the high-titanium tholeiitic basalt series, with a slightly right-inclined rare earth element distribution pattern, enriched in light rare earth elements (LREE) and incompatible elements such as Rb, Ba, and Th, which are similar to the characteristics of typical ocean island basalts (OIB), and their tectonic setting was formed in an extensional tectonic environment. Combined with the field occurrence and rock assemblage characteristics, it is considered to be a set of ocean island - seamount assemblages. Conclusions:Based on the comprehensive analysis of the geochemical characteristics of regional volcanic rocks in Yunnan and Guangxi, paleomagnetism, sponge spicule cherts, and sedimentary characteristics of radiolarian cherts, this paper holds that the Southeast Yunnan area of the Youjiang Basin had developed into a mature and complex multi-island ocean basin system during the Middle - Late Permian. This further provides new volcanic rock evidence for reconstructing the geological evolution process of the Late Paleozoic ocean basin in Southeast Yunnan, and confirms the existence of an ocean basin system in Southeast Yunnan during the Middle - Late Permian.