Abstract: Survey and research are carried out on the geologic characteristics such as stratigraphy, structure and wallrock alteration for the bentonite deposits around the Dayangshu area in Inner Mongolia. It is clarified that the orebodies occur in the lithic-crystal tuff and breccia of Longjiang formation, Lower Cretaceous. The orebodies are in two separate parts. By the depths and ore-forming conditions, the orebody in the east part can be divided into four layers; while that in the west, three layers. Based on the physical and chemical analysis for the ore, the bentonite in the area is recognized as calciumbased montmorillonite type, genetically formed by volcanic debris alteration.