Celaomiao Depression, east margin of Bayingebi Basins, is situated to the north of Mount Langshan, in Urad Rear Banner（Wulate Houqi), west of Inner Mongolia, China. The Depression is filled with Cretaceous clastic rocks and covers 850km2. The authors of this article have found a small volcanic vent filled with alkli syenites and basalts enclosed with hornfels outcropped in the southern margin. The outcrop is 185m long in the NEE trending and 55m wide in the NNW direction and extruded for 20m more than the surrounding sedimentary rocks. The igneous rocks of different types inside the vent show clear zonations. The center is a lenticular intrusive body (1m wide) of light colored syenite trending in NEE; a zone of 10m wide encircling the central syenite is composed of dark colored syenite, and the outmost zone of more than 10m wide is black basalt with horizontal columnar jointing structures perpendicular to the vertical wall of baked clastic rocks outside of the igneous rocks. There is a diabase dike of 2m wide across the vent in the W—E orientation. Obviously, the light color syenite—dark color syenite—basalt filled in the volcanic vent and the diabase dike across the vent are originated from the same mafic magma and separated through crystal fractionation during cooling process in the crust. The tectonic setting of this magmatism is still unclear. However, the outcrop is a typical example of volcanic conduit for geologists to investigate in detail and a nice site for geological field training.