The alkali feldspar syenite in Zhuxi Manjinggou, which is located in the south Qinling orogenic belt, intruded into the disbase body in small lenticular form. Locally, it intruded into Early Paleozoic strata. A study of its petrological characteristics and geochemical characteristics reveals the followings characteristics:the alkali feldspar syenite in this area is potassic alkaline syenite with high total alkali (Na₂O+K₂O); the Mg^# in the rock is obviously lower than that in the original magma, which indicates that the magma experienced a high degree evolution; the REE in the body is high, and exhibits LREE enrichment and HREE depletion. The trace element diagrams show that the syenite in this area originated from early continental rift environment in the Early Silurian.