Abstract: The intermediate volcanic rocks of Middle Permian Dashizai Formation outcropping in Tuquan area, Inner Mongolia were identified to be keratophyre by thin-section determination and feldspar component analysis. This paper describes in detail the visual and microscopic characteristics of the keratophyre samples, with analysis of the chemical composition of feldspar by electron probe technology and calculation of its crystal chemical formula. Study shows that the feldspar is composed of more than 95% of albite and less than 5% of anorthite and potash feldspar. Thus the feldspar is determined as albite. The Ab-An-Or diagram also confirms that the feldspar in the intermediate volcanic rocks is albite. The discovery of keratophyre provides the petrologic evidence for further studies on regional geotectonic evolution history of Late Paleozoic epoch in the mid-south of Daxinganling region.