The ophiolite zone in Sanmen area of Longsheng district, Guangxi is tec- topically located at the south-west terminal of the Jiangnan Geoanticline. The stratigraphic sequence in the area includes Hetong Formation and Gong- dong Formation of Upper Banxi Group of Pre-Sinian System, and also Sinian and Cambrian Systems. The spilites occur in the upper member of Hetong Formation. Some deep sea silicolites, shales, and a minor amount of carbonatites are involved in the spilites. In the area where spilites are distributed, there are a large amounts of diabases, and a minor amounts of basic-ultrabasic and ultrabasic complexes. The variation diagram of the chemical compositions of the volcanic rocks- (Fe0)/Mg0 to Si02 indicates that the volcanic rocks in this area are of talc-alkali series (CA) and tholeiite series (TH)，thus the ophiolites belong to the I type which was divided by A. Miyashiro. In the Ti-Zr variation dia- gram, the dots marking the compositions of the volcanic rocks also lie in the field of island arcs. Furthermore, the contents of trace elements in the volcan- ic rocks are very similar to the TH series and the CA series of the island arcs. It is suggested that the ophiolites in this area were formed in ancient island arc environments.